Abstract

The genus Calyptogena (Bivalvia: Vesicomyidae) comprises highly specialized bivalves living in symbiosis with sulphur-oxidizing bacteria in reducing habitats. In this study, the genus is revised using shell and anatomical features. The work is based on type material, as well as on the extensive collection of vesicomyids obtained during twelve expeditions to the Pacific and Indian Oceans. Nine Recent species are ascribed to the genus Calyptogena, four of which are new: C. pacifica Dall, 1891, C. fausta Okutani, Fujikura & Hashimoto, 1993, C. rectimargo Scarlato, 1981, C. valdiviae (Thiele & Jaeckel, 1931), C. gallardoi Sellanes & Krylova, 2005, C. goffrediae n. sp., C. starobogatovi n. sp., C. makranensis n. sp. and C. costaricana n. sp. The characteristic features of Calyptogena are: shell up to 90 mm in length, elongate-elliptical or elongate; presence of escutcheon; presence of broad posterior ramus (3b) of right subumbonal cardinal tooth as well as right posterior nymphal ridge; absence of pallial sinus as a result of attachment of intersiphonal septal retractor immediately adjacent to ventral surface of posterior adductor; absence of processes on inner vulva of inhalant siphon; presence of inner demibranch only, with descending and ascending lamellae with interlamellar septa not divided into separate tubes. The most closely related taxa to Calyptogena are probably the genus Isorropodon Sturany, 1896, and the group of species represented by ‘Calyptogenaphaseoliformis Métivier, Okutani & Ohta, 1986. These groups have several characters in common, namely absence of pallial sinus, presence of single inner pair of demibranchs and absence of processes on inner vulva of inhalant siphon. The worldwide distribution of the genus Calyptogena suggests that methane seeps at continental margins are the major dispersal routes and that speciation was promoted by geographical isolation. Recent species diversity and fossil records indicate that the genus originated in the Pacific Ocean. Sufficient data to discuss the distribution at species level exist only for C. pacifica, which has a remarkably narrow bathymetric range. Published studies on the physiology of C. pacifica suggest that adaptation to a specific geochemical environment has led to coexisting vesicomyid genera. The bacteria-containing gill of C. pacifica and other Calyptogena species is one of the most specialized in the family Vesicomyidae and may reflect these ecological adaptations.

INTRODUCTION

The family Vesicomyidae includes highly specialized bivalves known worldwide from continental slopes to hadal depths. Most, if not all, species of the family occur in reducing sulphide-rich habitats such as cold seeps, hydrothermal vents and whale carcasses, where they are often dominant in these chemosynthesis-based communities (Boss & Turner, 1980; Turner, 1985; Cosel & Salas, 2001; Krylova, 2002). All investigated vesicomyids harbour chemoautotrophic bacteria in their gills on which their nutrition depends (Fisher, 1990). Vesicomyids have been the subject of numerous studies involving physiological, biochemical, genetic, ecological and biogeographical approaches. In spite of this attention, the taxonomy of vesicomyids is far from being settled, both at species and supraspecific levels (Boss & Turner, 1980; Peek et al., 1997; Goffredi et al., 2003). The problematic taxonomy of this important group of animals frustrates the overall ecological and biogeographical investigation of chemosynthesis-based communities. Different authors estimate that the family includes from 50 to more than 70 Recent and fossil species (Peek et al., 1997; Cosel & Salas, 2001; Goffredi et al., 2003). Differences in the estimations of the species number reflect the uncertainties of taxonomic assignments.

The type genus of the family Vesicomyidae Dall & Simpson, 1901, VesicomyaDall, 1886, has similarities with Kelliella M. Sars, 1870, which is the type genus of the family Kelliellidae P. Fischer, 1887. If these two genera were united in the same family, the name Kelliellidae would take priority over Vesicomyidae. Relationships between these two groups have been debated for many years. Some authors have considered kelliellids and vesicomyids to be separate families (Dall, 1908; Thiele & Jaekel, 1931; Prashad, 1932; Woodring, 1938; Boss, 1967, 1968, 1970; Keen, 1969; Filatova, 1971; Bernard, 1974; Boss & Turner, 1980; Scarlato, 1981; Okutani, Fujikura & Kojima, 2000; Cosel & Salas, 2001), while others have united them (Thiele, 1935; Odhner, 1960; Clarke, 1962; Knudsen, 1970; Egorova, 1998; Allen, 2001).

The generic composition of the family has also been in question. Generic and subgeneric names of Recent and fossil groups that have been utilized are: AkebiconchaKuroda, 1943, ArchivesicaDall, 1908, CallogoniaDall, 1889, CalyptogenaDall, 1891, EctenagenaWoodring, 1938, HubertschenckiaTakeda, 1953, IsorropodonSturany, 1896, PhreagenaWoodring, 1938, Pleurophopsisvan Winkle, 1919, PliocardiaWoodring, 1925, VeneriglossaDall, 1886, VesicomyaDall, 1886 and WaisiuconchaBeets, 1942 (see Table 12). Different authors have recognized from one to twelve genera and subgenera, by synonymizing part of them or placing some genera into other families (Dall, 1908; Woodring, 1938; Odhner, 1960; Keen, 1969; Bernard, 1974; Boss & Turner, 1980; Okutani et al., 2000; Coan, Scott & Bernard, 2000; Allen, 2001; Cosel & Salas, 2001). Bernard (1974) proposed synonymizing Ectenagena and Akebiconcha with Archivesica. Boss & Turner (1980) synonymized Pleurophopsis, Phreagena, Ectenagena, Akebiconcha and Hubertschenckia with Calyptogena, and Archivesica with Callogonia. Vesicomyids from the Sea of Okhotsk have been assigned to Calyptogena, Waisiuconcha, Akebiconcha and Archivesica (Scarlato, 1981). Cosel & Salas (2001) showed that the genus Isorropodon, which has been placed in the family Trapeziidae, is a valid taxon of Vesicomyidae, and have assigned eastern Atlantic vesicomyids to Vesicomya, Waisiuconcha, Isorropodon and Callogonia. Allen (2001) synonymized Vesicomya with Kelliella and supposed that the genera and subgenera Akebiconcha, Archivesica, Callogonia, Calyptogena, Ectenagena and Phreagena were separated from Kelliella at least at subfamily level.

On the basis of shell morphology, Recent species have usually been assigned to Vesicomya, Calyptogena s.l. or Ectenagena (Boss, 1968; Boss & Turner, 1980; Okutani & Métivier, 1986; Krylova & Moskalev, 1996; Okutani et al., 1997; Barry & Kochevar, 1999; Okutani et al., 2000). However, there is much confusion in assignment of vesicomyid species to genera and molecular studies have revealed that the present genera do not comprise monophyletic species groups (Vrijenhoek et al., 1994; Kojima et al., 1995; Peek et al., 1997, Kojima et al., 2004). Coan et al. (2000) considered Calyptogena s.l. and Ectenagena to be ‘poorly defined’ taxa and at the present state of knowledge of vesicomyid taxonomy suggested using a single genus name, Vesicomya, for all species of the family. Some authors have followed this recommendation (Goffredi et al., 2003).

Nevertheless, in current literature dealing with chemosynthesis-based communities, Calyptogena is one of the most frequently used names, often for any large white clams. As a result, Calyptogena has become an inflated taxon combining phylogenetically distantly related species. At the same time, molecular studies have revealed that vesicomyids from the eastern Pacific which are usually attributed to Calyptogena pacifica, the type species of the genus, are actually composed of several morphologically cryptic species (Vrijenhoek et al., 1994; Peek et al., 1997). Recent studies have shown that the cryptic-species complex including C. pacifica contains at least five discrete evolutionary lineages (Goffredi et al., 2003). Clearly, Calyptogena needs an entire revision with an improved diagnosis based on both shell and anatomical features.

In this study, we attempt a taxonomic revision of Calyptogena s.s., which we regard as a separate genus in the family Vesicomyidae. The work is based on type material as well as on the extensive collection of vesicomyids obtained during twelve expeditions to the Pacific and Indian Ocean. The type species, C. pacifica, is redescribed based on the internal morphology. The paper includes a thorough description of C. fausta, C. rectimargo and C. gallardoi as well as four species that are new to science. Furthermore, we propose that C. valdiviae and V. longa are synonymous and that C. valdiviae is the appropriate species name.

We use a restrictive definition of the genus Calyptogena, which is in contrast to the ostensible likeness of the vesicomyid clams in general and the common use of the name ‘Calyptogena’ in many studies. However, we found that the genus Calyptogena s.s. is a clearly defined taxon characterized by a set of conchological and anatomical features comprising species with common adaptive strategies. The results suggest that Calyptogena s.s. is a monophyletic group within the family Vesicomyidae, which is supporterd by molecular data. We are faced with the problem that the other vesicomyid genera are not yet well defined. As a consequence, we exclude species which have previously been ascribed to Calyptogena, without proposing to which other genera they should belong. This is the subject of future work. Despite the fact that the other genera in the family Vesicomyidae are yet not well defined, we summarize their main characters based on current knowledge.

This revision of the genus Calyptogena s.s. is a first step towards a revision of the family Vesicomyidae. Phylogenetic studies on available vesicomyid species are underway and will be published separately. Detailed discussion of the relationships between Vesicomyidae and Kelliellidae needs further investigation of so-called ‘small vesicomyids’, and is beyond the scope of this paper.

MATERIAL AND METHODS

The examined material was collected during 12 expeditions (Table 1). Altogether the collection comprises seven species of which four are new. Material of one species consists of shells only, and samples of six species consist of preserved live-taken specimens. In addition, the type material of six described species was studied.

Table 1.

Summary of cruises during which samples were taken.

Research vessel Cruise no. Abbreviation Year Area 
Akademik Mstislav Keldysh 12 Keldysh 12 1986 Axial Seamount, Juan de Fuca Ridge 
Akademik Mstislav Keldysh 22 Keldysh 22 1990 Piip Volcano, Bering Sea 
Sonne 109 SO 109 1996 Continental margin off Oregon 
Sonne 110 SO 110 1996 Continental margin off Oregon 
Sonne 130 SO 130 1998 Makran Continental margin off Pakistan 
Sonne 143 SO 143 1999 Continental margin off Oregon 
Sonne 146 SO 146 2000 Continental margin off Peru 
Meteor 54 M 54 2002 Continental margin off Costa Rica 
Akademik M.A. Lavrentyev 28 Lv 28 1998 Sea of Okhotsk 
Marshal Gelovani Ge99 1999 Sea of Okhotsk 
Atlantis 131 At 131 1993 Continental margin off Oregon 
Atlantis 9906 AT9906 1999 Continental margin off Oregon 
Research vessel Cruise no. Abbreviation Year Area 
Akademik Mstislav Keldysh 12 Keldysh 12 1986 Axial Seamount, Juan de Fuca Ridge 
Akademik Mstislav Keldysh 22 Keldysh 22 1990 Piip Volcano, Bering Sea 
Sonne 109 SO 109 1996 Continental margin off Oregon 
Sonne 110 SO 110 1996 Continental margin off Oregon 
Sonne 130 SO 130 1998 Makran Continental margin off Pakistan 
Sonne 143 SO 143 1999 Continental margin off Oregon 
Sonne 146 SO 146 2000 Continental margin off Peru 
Meteor 54 M 54 2002 Continental margin off Costa Rica 
Akademik M.A. Lavrentyev 28 Lv 28 1998 Sea of Okhotsk 
Marshal Gelovani Ge99 1999 Sea of Okhotsk 
Atlantis 131 At 131 1993 Continental margin off Oregon 
Atlantis 9906 AT9906 1999 Continental margin off Oregon 

For refining of anatomical details, material of species from other genera was used (Table 2).

Table 2.

Additional vesicomyid species studied.

 Source of material 
Calyptogena (Archivesica) edisonensis Okutani, Kojima & Kim, 2004 SO 133, GTVA 34, 03°19.021′S, 152°34.849′E, 1448–1484 m 
Calyptogena (Archivesica) kilmeriBernard, 1974 SO 109/2, TVG 115, 44°40′1 N, 125°06′ W, 618 m 
Calyptogena (Ectenagena) laubieriOkutani & Métivier, 1986 Kaikoi, Dive KD 5, 33°36.9′N, 137°32.0′E, 3830 m, paratype, MNHN 
Calyptogena nankaiensisOkutani, Kojima & Ashi, 1996 JAMSTEC, Dive #897, 34°11.50′N, 137°45.50′E, 1911 m 
Calyptogena similarisOkutani, Kojima & Ashi, 1997 Shinkai 6500, Dive #587, 33°40.557′N, 136°33.938′E, 1100 m 
 Source of material 
Calyptogena (Archivesica) edisonensis Okutani, Kojima & Kim, 2004 SO 133, GTVA 34, 03°19.021′S, 152°34.849′E, 1448–1484 m 
Calyptogena (Archivesica) kilmeriBernard, 1974 SO 109/2, TVG 115, 44°40′1 N, 125°06′ W, 618 m 
Calyptogena (Ectenagena) laubieriOkutani & Métivier, 1986 Kaikoi, Dive KD 5, 33°36.9′N, 137°32.0′E, 3830 m, paratype, MNHN 
Calyptogena nankaiensisOkutani, Kojima & Ashi, 1996 JAMSTEC, Dive #897, 34°11.50′N, 137°45.50′E, 1911 m 
Calyptogena similarisOkutani, Kojima & Ashi, 1997 Shinkai 6500, Dive #587, 33°40.557′N, 136°33.938′E, 1100 m 

For the morphological descriptions, the following measurements (Fig. 1) were made with callipers (±0.1 mm): length of valve (L), height of valve (H), width of valve (W), length of fibrous part of ligament (F), length of posterior lamellar part of ligament (N). The position of the umbo was defined as the distance of the umbo from the anterior margin relative to the shell length (Um, in %). The terminology of Bernard (1895, 1896, 1897), described in detail in Cox (1969), was applied to the description of the hinge teeth (Fig. 2). This terminology was modified for the hinge of vesicomyids by Okutani (1966) and is widely used in recent literature on the vesicomyids (Horikoshi, 1989; Okutani et al., 2000; Cosel & Salas, 2002). The posterior elongated ridge on the nymphal callosity of the right valve of Calyptogena is usually classified as a lateral tooth, although its origin is unknown. Here we designated it as posterior nymphal ridge. Gross anatomy was observed on preserved live-taken specimens.

Figure 1.

Diagrammatic views of Calyptogena illustrating the terminology and measurements applied in this study. A. Right valve, internal view. B. Right valve, dorsal view. Abbreviations: aa, anterior adductor scar; ap, anterior pedal retractor scar; esc, escutcheon; F, fibrous ligament layer; H, height of valve; L, length of valve; lu, lunule; N, posterior lamellar ligament layer; pa, posterior adductor scar; pl, pallial line; U, distance from umbo to anterior margin; W, width of valve.

Figure 1.

Diagrammatic views of Calyptogena illustrating the terminology and measurements applied in this study. A. Right valve, internal view. B. Right valve, dorsal view. Abbreviations: aa, anterior adductor scar; ap, anterior pedal retractor scar; esc, escutcheon; F, fibrous ligament layer; H, height of valve; L, length of valve; lu, lunule; N, posterior lamellar ligament layer; pa, posterior adductor scar; pl, pallial line; U, distance from umbo to anterior margin; W, width of valve.

Figure 2.

Hinge margins in Calyptogena. A. Left valve. B. Right valve. Abbreviations: 1, ventral cardinal tooth; 2a, anterior ramus of subumbonal cardinal tooth; 2b, posterior ramus of subumbonal cardinal tooth; 3a, anterior ramus of subumbonal cardinal; 3b, posterior ramus of subumbonal cardinal; 3ba, anterior edge of 3b; 3 bp, posterior edge of 3b; ts, top surface of 3b; 4b, posterodorsal cardinal tooth; pnr, posterior nymphal ridge; all, anterior lamellar ligament layer; F, fibrous ligament layer; N, posterior lamellar ligament layer; ny, nymph.

Figure 2.

Hinge margins in Calyptogena. A. Left valve. B. Right valve. Abbreviations: 1, ventral cardinal tooth; 2a, anterior ramus of subumbonal cardinal tooth; 2b, posterior ramus of subumbonal cardinal tooth; 3a, anterior ramus of subumbonal cardinal; 3b, posterior ramus of subumbonal cardinal; 3ba, anterior edge of 3b; 3 bp, posterior edge of 3b; ts, top surface of 3b; 4b, posterodorsal cardinal tooth; pnr, posterior nymphal ridge; all, anterior lamellar ligament layer; F, fibrous ligament layer; N, posterior lamellar ligament layer; ny, nymph.

The type material is deposited in the Forschungsinstitut und Naturmuseum Senckenberg, Frankfurt a. M. (SMF) and Zoological Museum of Moscow State University, Moscow (ZMMU).

Abbreviations used in the text:

  • JAMSTEC, Japan Agency for Earth-Marine Science and Technology, Kanagawa

  • MNHNCL, National Museum of Natural History, Chile

  • MNHN, Muséum National d'Histoire Naturelle, Paris

  • NSMT, National Science Museum, Tokyo

  • SMF, Forschungsinstitut und Naturmuseum Senckenberg, Frankfurt a. M.

  • USNM, National Museum of Natural History, Smithsonian Institution, Washington, D.C.

  • ZIN RAN, Zoological Institute of Russian Academy of Sciences; St Petersburg

  • ZMB, Museum für Naturkunde der Humboldt-Universität Berlin, (formerly: Zoologisches Museum der Humboldt-Universität Berlin)

  • ZMMU, Zoological Museum of Moscow State University, Moscow

  • F, Length of fibrous ligament

  • H, Height of valve

  • L, Length of valve

  • N, Length of posterior lamellar ligament

  • RV, Research vessel

  • Spm, Specimen live-collected

  • V, Valve

  • s.l., Sensu lato

  • s.s., Sensu stricto

  • TVG, TV-guided grab

  • TV-MUC, TV-guided multicorer

  • Um, Position of umbo (defined above)

  • W, Width of valve

THE GENUS CALYPTOGENA

The nomenclatural history of Calyptogena is complicated and up to now the familial placement, composition and the level of the taxon has been the subject of discussion. The genus Calyptogena was erected by Dall (1891) for the species C. pacifica and placed in the family Carditidae. Calyptogena pacifica was the single representative of the genus until 1916, when one more species, C. elongata, was described by Dall. Woodring (1938) pointed out the similarity of the hinge structure of Calyptogena to that of vesicomyids, placing the genus in the family Vesicomyidae Dall & Simpson, 1901. He also, established two genera closely allied to Calyptogena, namely Ectenagena (type species C. elongataDall, 1916) and Phreagena (fossil type species P. lasiaWoodring, 1938). Then Woodring (written communication, 1952 in Winterer & Durham, 1962) indicated that Phreagena should be synonymized with Calyptogena. Later, Okutani (1966) discussed the taxonomic affinities of Calyptogena and treated Calyptogena and AkebiconchaKuroda, 1943 as separate genera belonging to the family Cyprinidae. Keen (1969) regarded Calyptogena s.s., Ectenagena and Phreagena as subgenera of Calyptogena in the family Vesicomyidae. Bernard (1974) suggested distinguishing two subgenera of Calyptogena: Calyptogena s.s. and Archivesica. He proposed that Calyptogena s.s. should be used for ‘heavy shelled forms with dehiscent periostraca and no vestige of the pallial sinus’ (Bernard, 1974).

Boss & Turner (1980) distinguished in Calyptogena s.l. two subgenera: Calyptogena s.s. and Ectenagena, which differ from each other mainly by details of the hinge teeth. Their list of species currently referable to the genus Calyptogena s.s. includes 12 species, six of which are Recent: C. pacifica, C. kawamurai (Kuroda, 1943), C. kilmeriBernard, 1974, C. ponderosaBoss, 1968, C. soyoaeOkutani, 1957 and C. valdiviae (Thiele & Jaeckel, 1931).

Okutani et al. (2000) placed the vesicomyids collected by the Japan Marine Science and Technology Center into two genera, Vesicomya and Calyptogena. In Calyptogena, they distinguished three subgenera: Calyptogena s.s., Archivesica and Ectenagena. According to the diagnosis, Calyptogena s.s. is characterized by thick short shell with apparent escutcheon, >-shaped subumbonal tooth overhanging ventral tooth on the right valve, >-shaped subumbonal tooth on the left valve and apparent posterior lateral tooth. Only one species, C. faustaOkutani, Fujikura & Hashimoto, 1993, was included in Calyptogena s.s.

In this paper, Calyptogena is regarded as a separate genus in the sense of Dall (1891), Woodring (1938) and Scarlato (1981) and corresponds to Calyptogena s.s. of Keen (1969), Bernard (1974) and Okutani et al. (2000).

SYSTEMATIC DESCRIPTIONS

Family Vesicomyidae Dall & Simpson, 1901

Vesicomyacidae Dall & Simpson, 1901.

Vesicomyidae Keen, 1969.

Genus CalyptogenaDall, 1891

CalyptogenaDall, 1891: 189.

CalyptogenaWoodring, 1938: 50.

Calyptogena (Calyptogena)Bernard, 1974: 11. Okutani et al., 2000: 94.

Calyptogena (Calyptogena)Boss & Turner, 1980: 185 (in part).

Type species: Calyptogena pacificaDall, 1891 (by monotypy).

Emended diagnosis: Shell usually medium-sized, L to 90 mm, from elongate-elliptical to elongate in outline, usually with nearly straight ventral margin. In nearly every species of genus there are two main variants in shape of posterior part of shell: one more expanded posterodorsally, the other with more elongated posterior part with sloping postero-dorsal margin. Escutcheon present, lunular incision indistinct or missing. Pallial line clearly visible, thick, with somewhat even margins, pallial sinus absent. Anterior adductor scar ovately triangular, somewhat impressed behind. Anterior pedal retractor scar not deeply impressed, located just above and behind anterior scar. Posterior adductor scar larger and less prominent than anterior adductor scar, pear-shaped, pointed dorsally, fused with posterior pedal retractor scar. Ligament external, parivincular, consisting of anterior and posterior lamellar layers and posterior fibrous layer. Anterior lamellar layer running from front of beak backwards behind posteriormost tooth just under fibrous layer, subumbonal pit absent. Posterior lamellar layer running from beak and overlain externally shorter fibrous layer, subtended by usually well-developed nymph. Dentition of right valve: ventral cardinal (1), subumbonal cardinal consisting of two rami (3a and 3b), 3b somewhat broad with anterior and posterior lamellate edges, and posterior nymphal ridge which may be nearly reduced or split into two parallel ridges. Dentition of left valve: subumbonal cardinal tooth with two rami (2a and 2b) and elongated posterodorsal cardinal tooth (4b). Ctenidia comprise inner demibranchs only with descending and ascending lamellae. Between lamellae there are fleshy septa. Retractor of intersiphonal septum fused with ventral surface of posterior adductor and attaches to shell immediately adjacent to it. Inner vulva of inhalant siphon does not bear processes.

Remarks: The genus Calyptogena differs from the genera Phreagena, Archivesica, Akebiconcha and Ectenagena by the presence of a broad 3b tooth and a right posterior nymphal ridge (see Table 12, Discussion). From Phreagena, Archivesica and Akebiconcha, it is also distinguished by an entire pallial line without a sinus. Additionally, from Archivesica, the genus Calyptogena differs by the presence of only inner demibranchs instead of both demibranchs, and by the absence of processes on the margin of the inner vulva of the inhalant siphon.

Calyptogena pacificaDall, 1891

(Figs 3–6)

Figure 3.

Calyptogena pacificaDall, 1891. A–H. RV Atlantis, Alvin dive 2646, L=38.00 mm. A. Exterior of left valve. B. Exterior of right valve. C. Interior of left valve. D. Interior of right valve. E. Left hinge plate. F. Right hinge plate. G. Dorsal view. H. Anterior view. I, J. RV Akademik Mstislav Keldysh, stn 2320, L=44.2 mm. I. Interior of left valve. J. Exterior of right valve.

Figure 3.

Calyptogena pacificaDall, 1891. A–H. RV Atlantis, Alvin dive 2646, L=38.00 mm. A. Exterior of left valve. B. Exterior of right valve. C. Interior of left valve. D. Interior of right valve. E. Left hinge plate. F. Right hinge plate. G. Dorsal view. H. Anterior view. I, J. RV Akademik Mstislav Keldysh, stn 2320, L=44.2 mm. I. Interior of left valve. J. Exterior of right valve.

Calyptogena pacificaDall, 1891: 190. Dall, 1895: 713, pl. 25, figs 4, 5. Woodring, 1938: 50. Okutani, 1966: 301, pl. 27, figs 1, 3. Boss, 1968: 739, figs 16, 17, 19, 20. Keen, 1969: N664, fig. E 138, 11a, b. Boss, 1970: 70.

Figure 4.

Calyptogena pacificaDall, 1891. A–D. Monterey Bay, L=53 mm. A. Exterior of left valve. B. Exterior of right valve. C. Interior of left valve. D. Interior of right valve. E–G.Sonne, stn 115, L=8.5 mm. E. Interior of left valve. F. Exterior of left valve. G. Interior of right valve. H–MSonne, stn 121, L=38.3 mm. H. Exterior of left valve. I. Anterior view. J. Exterior of right valve. K. Interior of left valve. L. Dorsal view. M. Interior of right valve.

Figure 4.

Calyptogena pacificaDall, 1891. A–D. Monterey Bay, L=53 mm. A. Exterior of left valve. B. Exterior of right valve. C. Interior of left valve. D. Interior of right valve. E–G.Sonne, stn 115, L=8.5 mm. E. Interior of left valve. F. Exterior of left valve. G. Interior of right valve. H–MSonne, stn 121, L=38.3 mm. H. Exterior of left valve. I. Anterior view. J. Exterior of right valve. K. Interior of left valve. L. Dorsal view. M. Interior of right valve.

Figure 5.

Calyptogena pacificaDall, 1891, RV Sonne, st. 187, L=25.2 mm. A. Soft parts as seen from left; L=26.5 mm: B. Soft parts as seen from left, left gill removed. Abbreviations: aa, anterior adductor muscle; al, ascending lamella of demibranch; alp, anterior labial palps; apr, anterior pedal retractor muscle; au, auricle; ddg, ductus of digestive gland; dg, digestive gland; dl, descending lamella of demibranch; es, exhalant siphon; f, foot; hg, hindgut; is, inhalant siphon; mm, mantle; mg, midgut; mo, mouth; o, ovarium; oe, oesophagus; pa, posterior adductor muscle; plp, posterior labial palps; ppr, posterior pedal retractor muscle; st, stomach; t, tentacles; v, ventricle.

Figure 5.

Calyptogena pacificaDall, 1891, RV Sonne, st. 187, L=25.2 mm. A. Soft parts as seen from left; L=26.5 mm: B. Soft parts as seen from left, left gill removed. Abbreviations: aa, anterior adductor muscle; al, ascending lamella of demibranch; alp, anterior labial palps; apr, anterior pedal retractor muscle; au, auricle; ddg, ductus of digestive gland; dg, digestive gland; dl, descending lamella of demibranch; es, exhalant siphon; f, foot; hg, hindgut; is, inhalant siphon; mm, mantle; mg, midgut; mo, mouth; o, ovarium; oe, oesophagus; pa, posterior adductor muscle; plp, posterior labial palps; ppr, posterior pedal retractor muscle; st, stomach; t, tentacles; v, ventricle.

Calyptogena (Calyptogena) pacificaBernard, 1974: 11, figs 1A, 2A, 3A, 4A–D. Boss & Turner, 1980: 188, figs 10B, C.

Vesicomya (Calyptogena) pacificaCoan et al., 2000: 341, pl. 70. Goffredi et al., 2003.

Type material: USNM 122549 (syntypes, 59 entire valves, 6 broken valves); USNM 222323 (syntypes, 6 valves); USNM 206424 (syntypes, 2 specimens with dry bodies). Type locality: East Pacific Ocean, Dixon Entrance, Alaska (55°46′N, 132°24′W), 322 fm (580 m) (Albatross Stn 3077).

Material examined: Type material. Monterey Bay, Mount Crushmore (36°47.1′N, 122°02.6′W, Barry et al. 1996), 630 m, 3 spm. RV Akademik Mstislav Keldysh, 22nd cruise, Stn 2320, MIR-2 dive 15/28, 55°23′N, 167°15′E, 489 m, 7 August 1990, 14 spms. RV Atlantis, Cruise 131, Alvin dive 2646, 44°40.56′N, 125°06.85′W, 720 m, 3 September 1993, 16 dry spms, 2 intact and 2 broken vs; Alvin dive 2653, 44°40.58′N, 125°07.48′W, 680 m, 12 September 1993, 4 dry spms. RV Atlantis, Cruise 9906, Stn AD8, Alvin dive 3422, 44°34.23′N, 125°08.90′W, 778 m, 3 July 1999, 4 spms; Stn AD11, Alvin dive 3423, 44°40′N, 125°06′W, 603 m, 4 July 1999, 1 wet spm, 1 dry spm, 5 vs; Stn AD14, Alvin dive 3424, 44°34.23′N, 125°08.90′W, 777 m, 5 July 1999, 10 wet spms, 35 dry spms; Stn AD25, Alvin dive 3427, 44°40.2′N, 125°05.9′W, 580 m, 8 July 1999, 1 dry spm, 2 intact and 5 broken vs; Stn AD28, Alvin dive 3428, 44°34.13′N, 125°09.15′W, 784 m, 9 July 1999, 1 intact and 4 broken vs; Stn AD32, Alvin dive 3429, 44°34′N, 125°09′W, 774 m, 10 July 1999, 3 wet spms, 10 dry spms, 2 broken vs. RV Sonne, Cruise 109/2, Stn 43/1, TVG, 44°40.44′N, 125°06.41′W, 637 m, 2 June 1996, 1 v; Stn 109, TVG; 44°40.17′N, 125°05.796′W, 598 m, 22 June 1996, 23 spms, many vs; Stn 115, TVG; 44°40′N, 125°06′W, 618 m, 22 June 1996, 206 wet, 76 dry spms, many vs; St 121, TVG; 44°40.17′N, 125°05.79′W, 627 m, 22 June 1999, many subfossil valves. RV Sonne, cruise 110/1A, stn 4, Ropos dive N 339, sample 415, 44°40.2′N, 125°06.5′W, 635 m, 10 July 1996, 4 vs; st 8, Ropos dive N 340, sample tray 2/3, 44°40.2′N, 125°05.9′W, 600 m, 11 July 1996, 46 spms, 20 vs; stn 9, TVG, 44°40.167′N, 125°05.873′W, 596 m, 12 July 1996, 14 wet spms, 83 dry spms, many vs; stn 11, TVG, 44°40.134′N, 125°06.503′W, 524 m, 12 July 1996, 14 spms, many vs. RV Sonne, cruise 143, stn 21-1, TVG, 44°34.222′N, 125°08.827′W, 786 m, 15 July 1999, 5 vs; stn 24, MUC, 44°34.223′N, 125°08.805′W, 787 m, 16 July 1999, 2 vs; stn 29-4C, MUC, 44°34.222′N, 125°08.817′W, 787 m, 18 July 1999, 12 dry spms; stn 41-1, TVG, 44°39.957′N, 125°06.091′W, 610 m, 20 July 1999, 7 dry spms, 6 vs; stn 55, MUC, 44°34.2′N, 125°08.85′W, 790 m, 24 July 1999, 13 dry spms; stn 68-2, TVG, 44°43.880′N, 125°13.864′W, 946 m, 27 July 1999, many dry spms, many vs; stn 71-1, TVG (B-10 cm), 44°34.2′N, 125°08.84′W, 787 m, 27 July 1999, 6 vs; stn 105-1F, TV-MUC, 44°34.218′N, 125°08.823′W, 787 m, 6 August 1999, 5 spms; stn 167, TVG, 44°50.263′N, 125°55.681′W, 567 m, 16 August 1999, 2 wet spms, 3 dry spms; stn 185-1, TV-MUC, 44°34.190′N, 125°08.830′ W, 787 m, 18 August 1999, 2 dry spms; stn 187-2H, TV-MUC, 44°34.180′N, 125°08.820′W, 786 m, 19 August 1999, 7 spms; stn 206-2B, TV-MUC, 44°34.182′N, 125°08.835′W, 787 m, 22 August 1999, 2 spms; stn 206-3D, TV-MUC, 44°34.472′N, 125°08.842′W, 786 m, 22 August 1999, 5 spms. RV Sonne, Cruise 148, Stn 74, Ropos dive 570, 44°34.1′N, 125°09.2′W, 570 m, 8 August 2000, 13 dry spms.

Diagnosis: Calyptogena species with L to 60 mm, stout, elongate-elliptical, H/L=0.56–0.65, W/L=0.18–0.25, ventral margin nearly straight along midpoint, with dehiscent dull periostracum, deep escutcheon, low umbo situated in anterior 24–31% of valve, prosogyrate beaks, stout nymph, fibrous layer of ligament occupying 20–34% of valve length and 61–80% of posterior lamellar layer, 4b-tooth occupying more than half of nymph length (Table 3).

Table 3.

Measurements of right valves of Calyptogena pacifica.

 L (mm) H (mm) W (mm) F (mm) N (mm) H/L W/L F/N F/L N/L Um (%) 
USNM no. 222323            
 Syntype 43.8 24.7 8.4 11.6 17.3 0.56 0.19 0.67 0.26 0.39 26 
 Syntype 39.2 23.3 7.8 12.5 17.8 0.59 0.20 0.70 0.32 0.45 27 
 Syntype 38.9 22.4 7.9 10.7 14.3 0.58 0.20 0.75 0.28 0.37 28 
USNM no. 122549            
 Syntype 54.7 32.3 11.5 19.3 24.2 0.59 0.21 0.80 0.35 0.44 28 
 Syntype 41.7 25.2 8.2 11.8 16.3 0.60 0.20 0.72 0.28 0.39 29 
 Syntype 40.8 23.0 8.1 11.8 16.3 0.56 0.20 0.72 0.29 0.40 27 
 Syntype 32.0 17.4 6.9 9.5 13.5 0.54 0.22 0.70 0.30 0.42 27 
 Syntype 30.4 18.2 6.7 8.2 10.7 0.60 0.22 0.77 0.27 0.35 30 
USNM no. 206424            
 Syntype 37.7 22.9 7.5 10.0 14.4 0.61 0.20 0.69 0.26 0.38 25 
 Syntype 28.2 17.8 5.9 6.4 10.8 0.63 0.21 0.59 0.23 0.38 29 
USNM no. 709147 29.7 17.7 5.2 6.0 10.7 0.60 0.18 0.56 0.20 0.36 29 
RV Sonne, stn 121 38.3 25.4 9.4 12.1 17.0 0.66 0.25 0.71 0.32 0.44 26 
RV Atlantis, dive 2646 38.0 24.5 7.3 10.3 16.8 0.64 0.19 0.61 0.27 0.44 30 
 36.3 21.7 8.2 12.4 18.8 0.60 0.23 0.66 0.34 0.52 26 
 35.3 22.7 7.8 10.3 15.1 0.64 0.22 0.68 0.29 0.43 27 
 33.5 19.5 6.3 10.5 14.5 0.58 0.19 0.72 0.31 0.43 30 
 32.9 19.4 6.6 9.2 13.0 0.59 0.20 0.71 0.28 0.40 25 
 32.9 19.9 6.2 8.0 12.0 0.60 0.19 0.67 0.24 0.36 24 
 32.5 20.4 6.4 9.8 15.0 0.63 0.18 0.65 0.30 0.46 22 
 29.2 16.9 5.4 8.1 11.6 0.58 0.18 0.70 0.28 0.40 27 
 27.2 17.0 5.3 6.7 11.0 0.62 0.19 0.61 0.27 0.40 25 
 19.9 12.4 3.6 4.0 7.1 0.62 0.18 0.56 0.20 0.36 31 
RV Keldysh, stn 2320 54.5 35.4 12.2 18.0 24.4 0.65 0.22 0.74 0.33 0.45 28 
 44.4 27.6 9.8 14.0 19.5 0.62 0.22 0.72 0.32 0.44 27 
 43.6 28.3 9.5 12.5 18.0 0.65 0.22 0.69 0.29 0.41 31 
 42.9 26.6 8.5 12.9 16.4 0.62 0.20 0.79 0.30 0.38 24 
 38.7 23.0 8.6 13.4 16.7 0.59 0.22 0.80 0.30 0.35 26 
 L (mm) H (mm) W (mm) F (mm) N (mm) H/L W/L F/N F/L N/L Um (%) 
USNM no. 222323            
 Syntype 43.8 24.7 8.4 11.6 17.3 0.56 0.19 0.67 0.26 0.39 26 
 Syntype 39.2 23.3 7.8 12.5 17.8 0.59 0.20 0.70 0.32 0.45 27 
 Syntype 38.9 22.4 7.9 10.7 14.3 0.58 0.20 0.75 0.28 0.37 28 
USNM no. 122549            
 Syntype 54.7 32.3 11.5 19.3 24.2 0.59 0.21 0.80 0.35 0.44 28 
 Syntype 41.7 25.2 8.2 11.8 16.3 0.60 0.20 0.72 0.28 0.39 29 
 Syntype 40.8 23.0 8.1 11.8 16.3 0.56 0.20 0.72 0.29 0.40 27 
 Syntype 32.0 17.4 6.9 9.5 13.5 0.54 0.22 0.70 0.30 0.42 27 
 Syntype 30.4 18.2 6.7 8.2 10.7 0.60 0.22 0.77 0.27 0.35 30 
USNM no. 206424            
 Syntype 37.7 22.9 7.5 10.0 14.4 0.61 0.20 0.69 0.26 0.38 25 
 Syntype 28.2 17.8 5.9 6.4 10.8 0.63 0.21 0.59 0.23 0.38 29 
USNM no. 709147 29.7 17.7 5.2 6.0 10.7 0.60 0.18 0.56 0.20 0.36 29 
RV Sonne, stn 121 38.3 25.4 9.4 12.1 17.0 0.66 0.25 0.71 0.32 0.44 26 
RV Atlantis, dive 2646 38.0 24.5 7.3 10.3 16.8 0.64 0.19 0.61 0.27 0.44 30 
 36.3 21.7 8.2 12.4 18.8 0.60 0.23 0.66 0.34 0.52 26 
 35.3 22.7 7.8 10.3 15.1 0.64 0.22 0.68 0.29 0.43 27 
 33.5 19.5 6.3 10.5 14.5 0.58 0.19 0.72 0.31 0.43 30 
 32.9 19.4 6.6 9.2 13.0 0.59 0.20 0.71 0.28 0.40 25 
 32.9 19.9 6.2 8.0 12.0 0.60 0.19 0.67 0.24 0.36 24 
 32.5 20.4 6.4 9.8 15.0 0.63 0.18 0.65 0.30 0.46 22 
 29.2 16.9 5.4 8.1 11.6 0.58 0.18 0.70 0.28 0.40 27 
 27.2 17.0 5.3 6.7 11.0 0.62 0.19 0.61 0.27 0.40 25 
 19.9 12.4 3.6 4.0 7.1 0.62 0.18 0.56 0.20 0.36 31 
RV Keldysh, stn 2320 54.5 35.4 12.2 18.0 24.4 0.65 0.22 0.74 0.33 0.45 28 
 44.4 27.6 9.8 14.0 19.5 0.62 0.22 0.72 0.32 0.44 27 
 43.6 28.3 9.5 12.5 18.0 0.65 0.22 0.69 0.29 0.41 31 
 42.9 26.6 8.5 12.9 16.4 0.62 0.20 0.79 0.30 0.38 24 
 38.7 23.0 8.6 13.4 16.7 0.59 0.22 0.80 0.30 0.35 26 

Description: Shell medium-sized, L to 60 mm, solid, elongate-elliptical in outline, equivalve. Periostracum thick, dehiscent, brownish, at periphery with up-standing, short, concentric lamellae, giving velvety appearance. Sculpture consisting of irregular growth lines and low ridges. Nearly all shells corroded to varying extent, especially in umbonal region. Escutcheon deep. Inequilateral, umbo situated in anterior 24–31% of valve. Umbones prosogyrate, low, beaks not touching each other. Anterior margin rounded, ventral margin broadly convex with nearly straight region along ventral midpoint, posterior margin rounded, subtruncate, with postero-dorsal obtuse angle, posterior-dorsal margin slightly convex. Pallial line impressed. Anterior adductor scar ovate-triangular in outline, strongly impressed to rear. Posterior adductor scar more rounded, sometimes slightly impressed, but usually obsolete. Anterior pedal retractor scar shallowly impressed, located just above and behind anterior adductor scar. Posterior pedal retractor scar slightly impressed, fused to posterior adductor scar. Shell margin may be crenulate in anterior and ventral parts. Nymph strong, often with nearly abrupt posterior margin and weak lamellar-ligament fused just after it, fibrous layer of ligament occupying 20–34% of valve length and 61–80% of posterior lamellar layer. Dentition of right valve: ventral cardinal (1) stout, from wedge-like to shelf-like, radiates obliquely anterior; 3a-ramus lamellate, almost parallel to anterior-dorsal shell margin, nearly of same length as (1), more prominent in distal part, fused in its proximal part with anterior edge of 3b-ramus; 3b-ramus broad, with slightly concave top surface and lamellate anterior and posterior edges, posterior edge usually more developed and parallel to posterior nymphal ridge, anterior edge may not be parallel to posterior one; posterior nymphal ridge elongate, parallel to posterior-dorsal margin, more expressed in adult specimens and nearly indistinct in juveniles. Dentition of left valve: 2a-ramus lamellate, parallel to anterior-dorsal shell margin, fused in its proximal part with anterior edge of 2b-ramus; 2b-ramus broad, often with slightly rising anterior and posterior edges and concave top surface, radiates ventralwards; 4b-tooth elongate, lamellate in its proximal part, parallel posterior-dorsal shell margin and usually exceeds half of nymph length or more.

Anatomy: Mantle lobes, thin and transparent except at margins. Outer, middle and inner mantle folds present (Fig. 6F). Middle fold is duplicated, divided into internal and external sub-folds near frontal part of anterior adductor. External sub-fold of middle fold is simple and very thin, and borders periostracal groove. Internal sub-fold of middle fold is well developed, bears papillae, larger papillae particularly prevalent anterior-ventrally and posteriorly just below inhalant siphon. Above inner mantle fold there is a vascularized thickening of mantle lobe extending from anterior to posterior adductors. Just dorsal of this vascularized zone there is line of attachment of pallial muscles to shell with the posterior muscles particularly stout. Mantle fusion forms three pallial apertures, the pedal gape and two posterior siphonal openings. Pedal gape occupies entire ventral edge from middle of frontal surface of anterior adductor to base of inhalant siphon. Dorsal mantle fusion involves inner fold and both middle sub-folds. Both siphons are formed from fused inner and internal sub-fold of middle folds. Siphons are short, united over their entire length, the posterior part of mantle forming a muscular envelope around them (Fig. 6D). Inhalant and exhalant apertures of nearly equal size, the inhalant siphon more muscular. Inhalant siphon bears 2–4 rows of small tentacles, sometimes the number of rows of tentacles increases in dorsal part of siphon. Exhalant siphon bears fewer rows of tentacles, usually only one. Tentacles differ in size, with rows of larger tentacles located more proximally. Internally, inhalant siphon has on its dorsal side a ventrally directed, triangular flap of muscular tissue. Proximal lateral margin of inhalant siphon thickened. Exhalant siphon with an internal, thin, transparent sleeve. Between siphons there is a septum, which joins with dorsal edge of descending lamellae of ctenidia (Fig. 6C). Intersiphonal septal retractor originating in lateral parts of siphonal septum is fused with ventral surface of posterior adductor and attaches to shell immediately adjacent to it. Anterior and posterior adductor muscles large, posterior muscle oval in section, anterior adductor muscle more elongate.

Figure 6.

Calyptogena pacificaDall, 1891. Anatomical details. A. Ventral view of the labial palps. B. Heart and kidney. C. Interior view of posterior part of mantle cavity. D. Posterior part of the body. E. Medial part of ctenidium. F. Transverse section through mantle margin. Abbreviations: aa, anterior adductor muscle; al, ascending lamella of demibranch; alp, anterior labial palps; apn, anterior pallial nerve; au, auricle; dl, descending lamella of demibranch; dpk, distal portions of kidney; eka, external kidney aperture; es, exhalant siphon; esm, external sub-fold of middle mantle fold; f, foot; fg, food groove; ga, genital apertures; hg, hindgut; ifj, interfilamental junctions; ils, interlamellar septum; imf, inner mantle fold; is, inhalant siphon; ism, internal sub-fold of middle mantle fold; iss, intersiphonal septum; iv, inner vulva of inhalant siphon; lgm, line of fusion of dorsal margin of ascending demibranchs; lmis, lateral margin of inhalant siphon; mf, muscle fibres; mm, mantle; mme, mantle muscularized envelope; mo, mouth; ois, inner opening of inhalant siphon; omf, outer mantle fold; pa, posterior adductor muscle; pc, pericardial cavity; per, periostracum; plp, posterior labial palps; ppk, proximal portion of kidney; ppr, posterior pedal retractor muscle; r-p a, reno-pericardial aperture; ses, sleeve of exhalant siphon; sr, siphonal retractor; tal – trace of attachment of dorsal margin of ascending lamellar; v, ventricle; ve, blood vessel; vt, vascularized thickening.

Figure 6.

Calyptogena pacificaDall, 1891. Anatomical details. A. Ventral view of the labial palps. B. Heart and kidney. C. Interior view of posterior part of mantle cavity. D. Posterior part of the body. E. Medial part of ctenidium. F. Transverse section through mantle margin. Abbreviations: aa, anterior adductor muscle; al, ascending lamella of demibranch; alp, anterior labial palps; apn, anterior pallial nerve; au, auricle; dl, descending lamella of demibranch; dpk, distal portions of kidney; eka, external kidney aperture; es, exhalant siphon; esm, external sub-fold of middle mantle fold; f, foot; fg, food groove; ga, genital apertures; hg, hindgut; ifj, interfilamental junctions; ils, interlamellar septum; imf, inner mantle fold; is, inhalant siphon; ism, internal sub-fold of middle mantle fold; iss, intersiphonal septum; iv, inner vulva of inhalant siphon; lgm, line of fusion of dorsal margin of ascending demibranchs; lmis, lateral margin of inhalant siphon; mf, muscle fibres; mm, mantle; mme, mantle muscularized envelope; mo, mouth; ois, inner opening of inhalant siphon; omf, outer mantle fold; pa, posterior adductor muscle; pc, pericardial cavity; per, periostracum; plp, posterior labial palps; ppk, proximal portion of kidney; ppr, posterior pedal retractor muscle; r-p a, reno-pericardial aperture; ses, sleeve of exhalant siphon; sr, siphonal retractor; tal – trace of attachment of dorsal margin of ascending lamellar; v, ventricle; ve, blood vessel; vt, vascularized thickening.

Foot well developed, rugose in its ventral part, very muscular. Short and shallow byssal groove lies along mid-ventral line of foot and leads to byssal aperture. Aperture of small byssal gland located slightly anterior to heel. Anterior and posterior pedal retractor muscles bifurcate before attaching to shell; anterior pedal retractor muscles insert on shell just posterior and dorsally to anterior adductor muscle, posterior pedal retractor muscles insert on shell dorsally to posterior adductor muscle.

Ctenidia thick, nonplicate, comprising inner demibranch only, with descending and ascending lamellae; the latter half the size of former (Fig. 6E). Filaments of the same lamella connected with each other by interfilamental junctions. Filaments of ascending lamella fused with the filaments of descending lamella by interlamellar septa. Ventral margin of demibranch with shallow food groove.

Margins of ctenidia fused along all its length and dividing mantle cavity into exhalant and inhalant chambers entirely isolated from each other. Anteriormost filaments insert between palps, laterally gill connected by ctenidial axis with visceral mass and by dorsal margin of ascending lamellae with proximal part of foot. Posterior to foot, margin of ascending lamellae fused with each other. Ctenidial muscle arising in distal end of ctenidial axis and inserting on lateral parts of pericardial walls.

Labial palps reduced; outer palps consist of thickened ridge with small plications, running along anteriormost part of ctenidia, inner labial palps smaller, with longitudinal ridges on inner surface (Fig. 6A). Mouth small, rounded, located beneath posterior face of anterior adductor, opening into thin-walled oesophagus. Inner epithelium of oesophagus bears longitudinal folds. Oesophagus enters anterior part of stomach. Anterior half of stomach covered by digestive gland. Stomach thin-walled, small, elongate, with low ridges and grooves on all inner surfaces. Digestive gland opens into anterior part of stomach by ducts, located laterally and lateral-ventrally on right side and laterally on left side. There is no style sac. Midgut leaves postero-ventral end of stomach, running nearly straight without any loops, penetrating ventricle. Rectum ends in an anus located on posterior surface of posterior adductor muscle.

Pericardial cavity large, elongate; pericardial glands located on lateral walls of pericardium and posterior part of auricles. Ventricle thick-walled, muscular, surrounding rectum (Fig. 6B). Auricles thin-walled, triangular, opening into ventricle in its posterior third. Kidneys located between pericardium and posterior adductor muscle. Paired reno-pericardial apertures locate on ventral side of pericardium posteriorly to ostia of auricles (on level of posterior part of ventricle). Pericardial (proximal) portions of kidney tube-like, with ridged inner epithelium. Distal portions of kidney not connected with each other. External apertures open just posterior to genital apertures in excurrent chambers. Sexes separate, large gonads embedded in posterior-dorsal part of visceral mass, adjacent to digestive gland. Genital apertures slit-like, located in excurrent chambers near base of posterior pedal retractor.

Variation: Variations can be seen in the shape and colour of shells, details of sculpture and hinge line. The outline of the shell can be more or less elongate. As in all species of Calyptogena there is a variation in the shape of posterior part of shell: some are more expanded posterodorsally (Figs 3A, 3J, 4A), while others are more elongated with sloping postero-dorsal margin (Fig. 4H). This variation in C. pacifica was pointed out before by Coan et al. (2000) who suggested sexual dimorphism. The relative length of different layers of ligament varies remarkably. The lunular region is usually not impressed, but sometimes incisions that limit the lunule are developed. Hinge teeth also vary: the right cardinal (3a) can be nearly fused with antero-dorsal margin of shell and the right posterior nymphal ridge can be reduced. There are variations in some anatomical details: the number of rows of tentacles around the inhalant siphon varies from 2 to 4, and the number of rows of tentacles around the exhalant siphon can be 1 or 2.

Remarks: Our observations on the anatomy of C. pacifica differ from the description by Bernard (1974). We found in our examined material, as well as in the dried soft tissue of syntypes (USNM No 206424), only one inner demibranch in the ctenidium, whereas Bernard noted that C. pacifica has ctenidia with both inner and outer demibranchs. Furthermore, at the base of the inhalant siphon of C. pacifica there is no flap of tissue with dendritic processes, as pointed out by Bernard (1974).

Distribution: Barents Sea (Piipa volcano), northwestern Pacific, and in eastern Pacific from Dixon Entrance, Alaska to Monterey Bay, California, 489–946 m.

Calyptogena faustaOkutani, Fujikura & Hashimoto, 1993

(Fig. 7)

Figure 7.

Calyptogena faustaOkutani, Fujikura & Hashimoto, 1993, Shinkai 2000, Dive 596, holotype, USMT-Mo 69872, L=61.0 mm. A. Exterior of left valve. B. Exterior of right valve. C. Interior of left valve. D. Interior of right valve. E. Left hinge plate. F. Right hinge plate. G. Dorsal view. H. Anterior view.

Figure 7.

Calyptogena faustaOkutani, Fujikura & Hashimoto, 1993, Shinkai 2000, Dive 596, holotype, USMT-Mo 69872, L=61.0 mm. A. Exterior of left valve. B. Exterior of right valve. C. Interior of left valve. D. Interior of right valve. E. Left hinge plate. F. Right hinge plate. G. Dorsal view. H. Anterior view.

Calyptogena (Ectenagena) faustaOkutani, Fujikura & Hashimoto, 1993: 122, figs 2–5.

Calyptogena (Calyptogena) faustaOkutani, Fujikura & Kojima, 2000: 94.

Type material: USMT-Mo 69872 (holotype, 2 dry valves). Type locality: Suruga Bay, 34°55′N, 138°39′E, 1489 m, 29 March 1992 (Shinkai 2000 Dive 596).

Material examined: Holotype only.

Diagnosis: Calyptogena species with L to 70 mm, stout, elongate, H/L=0.50, W/L=0.14, nearly straight ventral margin, with adherent translucent glossy smooth periostracum becoming wrinkled towards periphery, shallow escutcheon, low umbo situated in anterior 26% of valve, prosogyrate beaks, strong nymph, fibrous layer of ligament occupying 30% of valve length and 66% of posterior lamellar layer, right posterior nymphal ridge split into two parallel ridges, 4b-tooth occupying more than half of nymph length (Table 4).

Table 4.

Measurements of right valves of Calyptogena fausta.

 L (mm) H (mm) W (mm) F (mm) N (mm) H/L W/L F/N F/L N/L Um (%) 
Holotype, USMT-Mo 69872 61.0 30.0 8.6 18.0 27.1 0.49 0.14 0.66 0.30 0.44 25 
 L (mm) H (mm) W (mm) F (mm) N (mm) H/L W/L F/N F/L N/L Um (%) 
Holotype, USMT-Mo 69872 61.0 30.0 8.6 18.0 27.1 0.49 0.14 0.66 0.30 0.44 25 

Description: Shell medium-sized, L to 70 mm, stout, elongate, equivalve. Periostracum adherent, thin, translucent and glossy in the umbonal region, thicker and wrinkled in marginal region. Sculpture of irregular growth lines and ridges. Escutcheon shallow, lunule indistinct. Inequilateral, umbo situated at 25% from anterior end of valve. Umbones prosogyrate, low. Beaks enrolled, nearly touching each other. Anterior and posterior margins rounded, posterior-dorsal margin has obtuse angle; ventral margin nearly straight, weakly concave. Pallial line distinct but barely impressed. Anterior adductor scar slightly impressed to rear. Posterior adductor clearly visible, shallowly impressed. Nymph strong, with smoothly sloping posterior end, fibrous ligament layer occupies 30% of valve length. Dentition of right valve: ventral cardinal (1) stout, shelf-like with two blunt points, radiates obliquely anteriorwards; 3a-ramus thin, lamellate, nearly parallel to anterior-dorsal shell margin, fused in its low proximal part with anterior edge of 3b-ramus; 3b-ramus broad, with slightly concave top surface and rising lamellate anterior and posterior edges; posterior nymphal ridge split into two low lamellate ridges, distal from which more elongated, parallel to posterior-dorsal margin, occupies nearly all length of nymph. Dentition of left valve: 2a-ramus shelf-like, radiates obliquely anterior, fused in its proximal part with proximal part of 2b-ramus; 2b-ramus broad, radiates ventralwards; 4b-tooth elongate, low and parallel to posterior-dorsal shell margin, occupying more that half of nymph length.

Remarks: The species is morphologically very close to C. rectimargo (Table 6). The holotype of C. fausta differs from C. rectimargo by the presence of a posterior nymphal ridge that is split into two low lamellate ridges, occupying more than half of the nymph length, by the more pointed, not truncated posterior margin, the less developed escutcheon and the adherent periostracum. The shape of the shell of C. fausta is also similar to that of C. makranensis n. sp., from which it differs by the presence of a posterior nymphal ridge that is split into two low lamellate ridges and more prominent umbo, which is placed more anteriorly.

Distribution: Suruga Bay and Yukie Ridge, western Pacific, 1,500–2,000 m (Kojima & Ohta, 1997).

Calyptogena rectimargoScarlato, 1981

(Figs 8, 9)

Figure 8.

Calyptogena rectimargoScarlato, 1981, RV Gagara, stn 231, holotype, ZIN RAN 9970, L=48.2 mm. A. Exterior of left valve. B. Exterior of right valve. C. Interior of left valve. D. Interior of right valve. E. Left hinge plate. F. Right hinge plate. G. Dorsal view. H. Anterior view.

Figure 8.

Calyptogena rectimargoScarlato, 1981, RV Gagara, stn 231, holotype, ZIN RAN 9970, L=48.2 mm. A. Exterior of left valve. B. Exterior of right valve. C. Interior of left valve. D. Interior of right valve. E. Left hinge plate. F. Right hinge plate. G. Dorsal view. H. Anterior view.

Figure 9.

Calyptogena rectimargoScarlato, 1981. A–H. RV Marshal Gelovani, stn 25-1, L=68.4 mm. A. Exterior of left valve. B. Exterior of right valve. C. Interior of left valve. D. Interior of right valve. E. Left hinge plate. F. Right hinge plate. G. Dorsal view. H. Anterior view. I–K. St 28-1, L=57.5 mm. I. Interior of left valve. J. Interior of right valve. K. Dorsal view.

Figure 9.

Calyptogena rectimargoScarlato, 1981. A–H. RV Marshal Gelovani, stn 25-1, L=68.4 mm. A. Exterior of left valve. B. Exterior of right valve. C. Interior of left valve. D. Interior of right valve. E. Left hinge plate. F. Right hinge plate. G. Dorsal view. H. Anterior view. I–K. St 28-1, L=57.5 mm. I. Interior of left valve. J. Interior of right valve. K. Dorsal view.

Calyptogena rectimargoScarlato, 1981: 390, fig. 410.

Type material: ZIN RAN 9970 (holotype, 2 dry valves). Type locality: East of north Sakhalin, 52°53′N, 144°54′E, 1643 m, 10 August 1932 (RV Gagara, St.231).

Material examined: Type material. RV Akademik M.A. Lavrentyev, Cruise 28, Stn 21-1, gravity corer, 54°26′N, 144°04′E, 702 m, 17 August 1998, 1 v, 1 broken v; Stn 36-1, dredge, 54°01′N, 146°15′E, 1490–1511 m, 20 August 1998, 1 sp; Stn 37-1, gravity corer, 53°59′N, 146°17′E, 1497 m, 20 August 1998, 2 vs, 4 broken vs; Stn 38-1, trawl, 54°05′N, 146°17′E, 1522–1642 m, 20 August 1998, 2 broken vs. RV Marshal Gelovani, Cruise 1, Stn 25-1, trawl, 54°26′N, 144°04′E, 700 m, 14 September 1999, 6 spms, 20 vs, 3 broken vs; Stn 28-1, trawl, 54°26′N, 144°04′E, 700 m, 14 September 1999, 2 spm, 30 vs, 34 broken vs; Stn 29-3, gravity-corer, 54°26′N, 144°04′E, 700 m, 15 September 1999, 8 vs, 8 broken vs.

Diagnosis: Calyptogena species with L to 70 mm, stout, elongate, H/L=0.45–0.56, W/L=0.14–0.20, ventral margin nearly straight, with dehiscent periostracum becoming strongly wrinkled towards the periphery, moderate escutcheon, low umbo situated in anterior 25–29% of valve, prosogyrate beaks, strong nymph, fibrous ligament layer occupying 24–40% of valve length and 55–77% of posterior lamellar layer, 4b-tooth occupying nearly half of nymph length (Table 5).

Table 5.

Measurements of right valves of Calyptogena rectimargo.

 L (mm) H (mm) W (mm) F (mm) N (mm) H/L W/L F/N F/L N/L Um (%) 
Holotype, ZIN RAN 9970 48.2 21.6 6.7 14.3 23.8 0.45 0.14 0.60 0.30 0.49 27 
RV Marshal Gelovani            
 stn 25-1 68.4 31.3 11.5 24.5 34.7 0.46 0.17 0.71 0.36 0.51 25 
 56.3 30.2 10.6 22.6 29.6 0.54 0.19 0.76 0.40 0.53 25 
 52.6 25.5 9.2 18.4 25.6 0.49 0.18 0.72 0.35 0.49 25 
 51.0 28.2 8.8 12.6 21.6 0.55 0.17 0.58 0.25 0.42 29 
 50.8 28.4 10.3 19.7 25.6 0.56 0.20 0.77 0.39 0.50 26 
 50.6 28.0 8.6 11.9 21.7 0.55 0.17 0.55 0.24 0.43 28 
 stn 28-1 57.5 30.8 10.1 21.3 29.2 0.54 0.18 0.73 0.37 0.51 26 
 43.4 23.3 7.0 11.3 19.7 0.54 0.16 0.57 0.26 0.45 29 
 L (mm) H (mm) W (mm) F (mm) N (mm) H/L W/L F/N F/L N/L Um (%) 
Holotype, ZIN RAN 9970 48.2 21.6 6.7 14.3 23.8 0.45 0.14 0.60 0.30 0.49 27 
RV Marshal Gelovani            
 stn 25-1 68.4 31.3 11.5 24.5 34.7 0.46 0.17 0.71 0.36 0.51 25 
 56.3 30.2 10.6 22.6 29.6 0.54 0.19 0.76 0.40 0.53 25 
 52.6 25.5 9.2 18.4 25.6 0.49 0.18 0.72 0.35 0.49 25 
 51.0 28.2 8.8 12.6 21.6 0.55 0.17 0.58 0.25 0.42 29 
 50.8 28.4 10.3 19.7 25.6 0.56 0.20 0.77 0.39 0.50 26 
 50.6 28.0 8.6 11.9 21.7 0.55 0.17 0.55 0.24 0.43 28 
 stn 28-1 57.5 30.8 10.1 21.3 29.2 0.54 0.18 0.73 0.37 0.51 26 
 43.4 23.3 7.0 11.3 19.7 0.54 0.16 0.57 0.26 0.45 29 

Description: Shell medium-sized, L to 70 mm, solid, from elongate-elliptical to subquadrate elongate in outline, equivalve. Periostracum thick, dehiscent, dirty brownish, with short, concentric, upstanding lamellae developed at the periphery. Sculpture consisting of irregular growth lines and ridges. Escutcheon moderate to shallow, lunular region sometimes impressed. Inequilateral, umbo situated at 25–29% from anterior end of valve. Umbones prosogyrate, low. Anterior margin rounded, posterior margin rounded-truncate; ventral margin nearly straight and parallel to dorsal. Pallial line impressed. Anterior adductor scar strongly impressed to rear. Posterior adductor clearly visible. Nymph strong, fibrous ligament layer occupies 25–40% of valve length. Dentition of right valve: ventral cardinal (1) stout, wedge-shaped, radiates obliquely anteriorly; 3a-ramus thin, lamellate, parallel to anterior-dorsal shell margin, sometimes very low and nearly reduced, fused in its proximal part with anterior edge of 3b-ramus; 3b-ramus broad, with lamellate anterior and posterior edges and slightly concave top surface, posterior edge usually more developed and parallel to posterior nymphal ridge, anterior edge may not be parallel to posterior one; posterior nymphal ridge elongate, low, more expressed in its distal part, occupies nearly half of nymph length. Dentition of left valve: 2a-ramus lamellate, sub-parallel to anterior-dorsal shell margin, fused in its proximal part with anterior edge of 2b-ramus; 2b-ramus broad, radiates ventralwards; 4b-tooth elongate, low and parallel to posterior-dorsal shell margin, occupying nearly half of nymph length.

Anatomy: All features of genus.

Variation: The shape of shell can be more or less elongated. There is some variation in the size of the escutcheon. The relative length of the different layers of the ligament varies remarkably.

Remarks: Based on the shape of the shell, C. rectimargo is most similar to C. fausta and C. makranensis n. sp. (Table 11). From the first species C. rectimargo differs by not having a split posterior lateral tooth in the right valve, a shorter 4b-tooth, which usually occupies not much more than half of the nymph, a more developed escutcheon and dehiscent periostracum. Calyptogena makranensis n. sp. differs from the present species by the lower umbo placed more medially.

Distribution: Sea of Okhotsk, east of north Sakhalin, 700–1,643 m.

Calyptogena valdiviae (Thiele & Jaeckel, 1931)

(Figs 10–13)

Figure 10.

Calyptogena valdiviae (Thiele & Jaeckel, 1931), RV Valdivia, stn 33, lectotype, ZMB 101.598a, L=59.2 mm. A. Exterior of left valve. B. Exterior of right valve. C. Interior of left valve. D. Interior of right valve. E. Left hinge plate. F. Right hinge plate. G. Dorsal view. H. Anterior view.

Figure 10.

Calyptogena valdiviae (Thiele & Jaeckel, 1931), RV Valdivia, stn 33, lectotype, ZMB 101.598a, L=59.2 mm. A. Exterior of left valve. B. Exterior of right valve. C. Interior of left valve. D. Interior of right valve. E. Left hinge plate. F. Right hinge plate. G. Dorsal view. H. Anterior view.

Figure 11.

Vesicomya longaThiele & Jaeckel, 1931 [=Calyptogena valdiviae (Thiele, & Jaeckel, 1931)], RV Valdivia, stn 33, holotype, ZMB 101.601, L=70.6 mm. A. Exterior of right valve. B. Interior of right valve. C. Dorsal view. D. Anterior view. E. Right hinge plate.

Figure 11.

Vesicomya longaThiele & Jaeckel, 1931 [=Calyptogena valdiviae (Thiele, & Jaeckel, 1931)], RV Valdivia, stn 33, holotype, ZMB 101.601, L=70.6 mm. A. Exterior of right valve. B. Interior of right valve. C. Dorsal view. D. Anterior view. E. Right hinge plate.

Figure 12.

A, B, J.Vesicomya longaThiele & Jaeckel, 1931 [=Calyptogena valdiviae (Thiele, & Jaeckel, 1931)], RV Valdivia, stn 63, ZMB 101.602, paratype, L=57.9 mm. A. Exterior of right valve. B. Interior of right valve. J. Dorsal view. C-I, K.Calyptogena valdiviae (Thiele & Jaeckel, 1931), Valdivia, stn 33, ZMB 101.598b. C, D, K. Paralectotype, L=61.9 mm. C. Exterior of right valve. D. Interior of right valve. K. Dorsal view. E, F. Paralectotype, L=50.2 mm. E. Exterior of right valve. F. Interior of right valve. G. Paralectotype, L=45.2 mm, exterior of right valve. H, I. Paralectotype, L=35.9 mm. H. Exterior of right valve. I. Interior of right valve.

Figure 12.

A, B, J.Vesicomya longaThiele & Jaeckel, 1931 [=Calyptogena valdiviae (Thiele, & Jaeckel, 1931)], RV Valdivia, stn 63, ZMB 101.602, paratype, L=57.9 mm. A. Exterior of right valve. B. Interior of right valve. J. Dorsal view. C-I, K.Calyptogena valdiviae (Thiele & Jaeckel, 1931), Valdivia, stn 33, ZMB 101.598b. C, D, K. Paralectotype, L=61.9 mm. C. Exterior of right valve. D. Interior of right valve. K. Dorsal view. E, F. Paralectotype, L=50.2 mm. E. Exterior of right valve. F. Interior of right valve. G. Paralectotype, L=45.2 mm, exterior of right valve. H, I. Paralectotype, L=35.9 mm. H. Exterior of right valve. I. Interior of right valve.

Figure 13.

A, B. Vesicomya longaThiele & Jaeckel, 1931 [=Calyptogena valdiviae (Thiele, Jaeckel, 1931)], RV Valdivia, stn 63, ZMB 101.602, paratype, L=63.3 mm. A. Exterior of left valve. B. Interior of left valve. C–H.Calyptogena valdiviae (Thiele, Jaeckel, 1931). RV Valdivia, stn 33, ZMB 101.598b. C, D. Paralectotype, L=47.5 mm. C. Exterior of left valve. D. Interior of left valve. E, F. Paralectotype, L=49.0 mm. E. Exterior of left valve. F. Interior of left valve. G, H. Paralectotype, L=45 mm. G. Exterior of left valve. H. Interior of left valve.

Figure 13.

A, B. Vesicomya longaThiele & Jaeckel, 1931 [=Calyptogena valdiviae (Thiele, Jaeckel, 1931)], RV Valdivia, stn 63, ZMB 101.602, paratype, L=63.3 mm. A. Exterior of left valve. B. Interior of left valve. C–H.Calyptogena valdiviae (Thiele, Jaeckel, 1931). RV Valdivia, stn 33, ZMB 101.598b. C, D. Paralectotype, L=47.5 mm. C. Exterior of left valve. D. Interior of left valve. E, F. Paralectotype, L=49.0 mm. E. Exterior of left valve. F. Interior of left valve. G, H. Paralectotype, L=45 mm. G. Exterior of left valve. H. Interior of left valve.

Vesicomya valdiviaeThiele & Jaeckel, 1931: 229, pl. 9(4), fig. 101.

Calyptogena valdiviaeBoss, 1968: 742. Boss, 1970: 69, figs 3, 4, 22, 25.

Calyptogena (Calyptogena) valdiviaeBoss & Turner, 1980: 190.

‘Vesicomya’ valdiviaeCosel & Salas, 2001: 362, figs 105.

Vesicomya longaThiele & Jaeckel, 1931: 229, pl. 9(4), fig. 103.

Vesicomya (Archivesica) longaBoss, 1970: 72, figs 11, 23, 26.

‘Vesicomya’ longaCosel & Salas, 2001: 363, figs 106.

Type material: Vesicomya valdiviae: ZMB 101.598a (lectotype, 2 valves of the same specimen, selected by Boss (1970)); ZMB 101.598b (paralectotypes, 31 valves, same locality); ZMB 101.599 (paralectotypes, 6 valves, RV Valdivia, Stn 103, 35°10.5′S, 23°02′E, 500 m). Type locality: about 230 km E of Morro Garnet, Rio de Oro, West Africa, East Atlantic Ocean, 24°35.3′N, 17°4.7′W, 2480 m, 25 August 1898 (RV Valdivia, Stn 33). Vesicomya longa: ZMB 101.601 (holotype, 1 right valve); ZMB 101.602 (paratypes, 6 intact valves and 2 broken valves, RV Valdivia, St 63, 2°N, 8°04.3′E, 2492 m).

Material examined: Type material.

Diagnosis: Calyptogena-species with L to 73 mm, stout, elongate-elliptical, H/L=0.56–0.65, W/L=0.19–0.26, with convex ventral margin, adherent, glossy, yellowish periostracum, rather deep escutcheon running along all dorsal-posterior margin, moderately low umbo situated in anterior 30–36% of valve length, prosogyrate beaks, moderately strong nymph, posterior lamellar layer of ligament encompassing 34–47% of length shell, 4b-tooth occupying nearly half of nymph length (Table 6).

Table 6.

Measurements of valves of Calyptogena valdiviae and Vesicomya longa.

 L (mm) H (mm) W (mm) N (mm) H/L W/L N/L Um (%) 
Lectotype V. valdiviae ZMB 101.598a         
 Right valve 59.2 38.4 12.6 27.8 0.65 0.21 0.47 31 
Paralectotypes V. valdiviae ZMB 101.598b         
 Right valve 61.9 37.6 14.5 28.0 0.61 0.23 0.45 33 
 Right valve 60.0 38.4 14.3 24.0 0.58 0.24 0.40 32 
 Right valve 55.0 34.5 11.5 22.2 0.63 0.21 0.40 33 
 Right valve 51.6 33.5 10.9 23.7 0.65 0.21 0.46 34 
 Right valve 50.2 29.2 12.3 19.3 0.58 0.26 0.38 34 
 Right valve 49.2 28.1 10.6 18.0 0.57 0.22 0.37 35 
 Left valve 49.0 31.3 10.8 20.0 0.63 0.22 0.41 35 
 Right valve 45.2 26.5 10.0 19.0 0.59 0.22 0.42 33 
 Left valve 45.0 26.0 9.9 15.0 0.58 0.22 0.33 33 
 Right valve 35.9 23.4 7.1 13.1 0.65 0.20 0.36 36 
Paralectotypes of V. valdiviae ZMB 101.599         
 Right valve 56.0 35.2 12.5 23.0 0.63 0.22 0.41 33 
 Right valve 45.4 27.2 12.0 17.4 0.60 0.26 0.38 36 
Holotype of V. longa ZMB101.601         
 Right valve 70.6 39.7 14.7 26.0 0.56 0.21 0.37 34 
Paratypes of V. longa ZMB 101.602         
 Right valve 73.1 42.0 16.0 29.5 0.57 0.22 0.40 35 
 Left valve 72.0 41.8 15.2 30.0 0.58 0.21 0.42 31 
 Left valve 71.3 42.5 15.7 31.3 0.60 0.22 0.44 31 
 Left valve 63.3 36.4 14.4 26.5 0.58 0.23 0.42 30 
 Left valve 61.2 34.2 11.5 21.0 0.56 0.19 0.34 32 
 Right valve 57.9 34.3 12.2 25.0 0.59 0.21 0.43 34 
 L (mm) H (mm) W (mm) N (mm) H/L W/L N/L Um (%) 
Lectotype V. valdiviae ZMB 101.598a         
 Right valve 59.2 38.4 12.6 27.8 0.65 0.21 0.47 31 
Paralectotypes V. valdiviae ZMB 101.598b         
 Right valve 61.9 37.6 14.5 28.0 0.61 0.23 0.45 33 
 Right valve 60.0 38.4 14.3 24.0 0.58 0.24 0.40 32 
 Right valve 55.0 34.5 11.5 22.2 0.63 0.21 0.40 33 
 Right valve 51.6 33.5 10.9 23.7 0.65 0.21 0.46 34 
 Right valve 50.2 29.2 12.3 19.3 0.58 0.26 0.38 34 
 Right valve 49.2 28.1 10.6 18.0 0.57 0.22 0.37 35 
 Left valve 49.0 31.3 10.8 20.0 0.63 0.22 0.41 35 
 Right valve 45.2 26.5 10.0 19.0 0.59 0.22 0.42 33 
 Left valve 45.0 26.0 9.9 15.0 0.58 0.22 0.33 33 
 Right valve 35.9 23.4 7.1 13.1 0.65 0.20 0.36 36 
Paralectotypes of V. valdiviae ZMB 101.599         
 Right valve 56.0 35.2 12.5 23.0 0.63 0.22 0.41 33 
 Right valve 45.4 27.2 12.0 17.4 0.60 0.26 0.38 36 
Holotype of V. longa ZMB101.601         
 Right valve 70.6 39.7 14.7 26.0 0.56 0.21 0.37 34 
Paratypes of V. longa ZMB 101.602         
 Right valve 73.1 42.0 16.0 29.5 0.57 0.22 0.40 35 
 Left valve 72.0 41.8 15.2 30.0 0.58 0.21 0.42 31 
 Left valve 71.3 42.5 15.7 31.3 0.60 0.22 0.44 31 
 Left valve 63.3 36.4 14.4 26.5 0.58 0.23 0.42 30 
 Left valve 61.2 34.2 11.5 21.0 0.56 0.19 0.34 32 
 Right valve 57.9 34.3 12.2 25.0 0.59 0.21 0.43 34 

Description: Shell medium-sized, L to 73 mm, solid, elongate-elliptical in outline, equivalve. Periostracum thin, adherent, glossy yellowish. Sculpture consisting of irregular growth lines and wrinkles. Escutcheon deep, bordered by sharp dorsal margin, running along all dorsal-posterior side, lunule impressed, indistinct, sometimes limited by shallow incision. Inequilateral, umbo situated 30–36% from anterior end of valve. Umbones prosogyrate, moderately low, beaks enrolled. Anterior-dorsal margin slightly concave and sometimes forms rounded angle with anterior margin, anterior-ventral margin broadly rounded, ventral margin slightly convex, posterior margin rounded-truncate, posterior-dorsal margin usually slightly convex. Pallial line clearly visible, sometimes impressed, more strongly in its anterior part. Anterior adductor scar impressed to rear. Posterior adductor clearly visible, sometimes slightly impressed. Anterior pedal retractor scar shallowly impressed. Nymph moderately strong, with sloping posterior end. Dentition of right valve: ventral cardinal (1) stout, wedge-shaped, radiates obliquely anterior; 3a-ramus lamellate, low, parallel to anterior-dorsal shell margin, fused in its proximal part with anterior edge of 3b-ramus; 3b-ramus broad, low, with slightly rising anterior and posterior edges and therefore concave top surface, anterior edge usually radiates ventrally, posterior edge parallel to posterior nymphal ridge; posterior nymphal ridge elongate, parallel to posterior-dorsal margin. Dentition of left valve: 2a-ramus shelf-like, parallel to anterior-dorsal shell margin or slightly radiates anterior-ventrally, fused in its proximal part with proximal part of 2b-ramus; 2b-ramus thicker than 2a, radiates ventral-wards; 4b-tooth elongate and parallel to posterior-dorsal shell margin, occupying nearly half of nymph length.

Variation: Variations are seen in the thickness and shape of valves, details of sculpture and dental configuration. The thickness of valves varies from heavy to moderate; the specimens described as V. longa are usually more thin-shelled. The escutcheon can be from moderately impressed to deep. The lunular incision, which sometimes limits the lunule, varies from shallow to deep (the deepest one is in the holotype of V. longa).

The shape of the shell can be more or less elongate. The position of the umbo and the lengths of the fibrous layers of the ligament vary. The right 3a-ramus can be nearly fused with the antero-dorsal margin, and therefore be indistinct; the posterior nymphal ridge can be reduced. In the left valve, the shape of 2a-ramus varies from lamellate to shelf-like and the angle between 2a- and 2b- rami can range from acute to obtuse. Sometimes the hinge margin is strongly corroded. Two usual main variants in the shape of posterior part of shell are: a more expanded (Figs 10A, 12A) and more elongated form with sloping postero-dorsal margin (Fig. 12E, G).

Remarks: Redescriptions of Vesicomya valdiviae and V. longa were made by Boss (1970). He selected a lectotype of V. valdiviae, compared it with C. pacifica and emphasized the similarity between them in the heaviness of the valves, dental configuration and ‘weakly sinuate pallial line’, which ‘are all typical of Calyptogena’. On this evidence, he placed V. valdiviae in Calyptogena. Furthermore, Boss (1970) compared V. longa with V. suavisDall, 1913 and found that they have much in common. Since Boss (1970) placed V. suavisDall, 1913 in ArchivesicaDall, 1925, V. longa was also provisionally assigned to Archivesica.

Our own comparison of V. longa with the holotype of V. suavis showed that these two species are remarkably different; for example, a pallial sinus is present in V. suavis, but absent in V. longa; an escutcheon is absent in V. suavis, but present in V. longa. Moreover, both species have different hinge margins. 

In addition, we compared V. longa with Archivesica gigasDall, 1895, the type species of the genus Archivesica and found differences between these two species. Firstly, A. gigas has an indistinct pallial line with a weak sinus, whereas the pallial line of V. longa is clearly visible, sometimes even impressed, and entire. Secondly, there are differences in the hinge structure: in A. gigas, the proximal part of the anterior lamellar ligament is placed in a special excavation, the subumbonal pit, just above the posterior hinge tooth, whereas in V. longa the subumbonal pit is absent; the 3b-ramus of the right valve of A. gigas is thin and lamellate and the posterior nymphal ridge is absent, whereas 3b-ramus of V. longa is broad, with concave top surface and slightly rising anterior and posterior ridges and the posterior nymphal ridge is present. Thirdly, A. gigas has no escutcheon, while in V. longa it is deep and long. These differences clearly demonstrate that V. longa should not be included in the genus Archivesica.

The shells selected as the types of V. longa and V. valdiviae were collected at the same station and represent near extreme variants in the range of variability of the available material. The main differences between the right valves of the types of V. longa and V. valdiviae are manifested in the thickness of valves, in the outline of shell (height/length ratio) and the extent of development of teeth, all of these features more or less fit the range of the variation observed in the paratypes. Some of these differences can be explained by allometric changes, since the length of specimens of V. valdiviae ranges from 36 to 62 mm, while the specimens of V. longa are larger ranging from 58 to 73 mm. This comparison of V. longa with V. valdiviae shows that the differences between these two forms fall within the usual range of the intraspecific variation of vesicomyids, and we therefore synonymize the two species.

Distribution: East Atlantic Ocean: off Morocco, 2480 m; Gulf of Guinea, 2492 m; off Knysna, Republic of South Africa, 500 m.

Calyptogena gallardoiSellanes & Krylova, 2l005

(Fig 14)

Figure 14.

Calyptogena gallardoiSellanes & Krylova, 2005, RV Kay Kay, stn 40, holotype, MNHNCL-200734, L=41.3 mm. A. Exterior of left valve. B. Exterior of right valve. C. Interior of left valve. D. Interior of right valve. E. Left hinge plate. F. Right hinge plate. G. Dorsal view of left valve. H. Anterior view.

Figure 14.

Calyptogena gallardoiSellanes & Krylova, 2005, RV Kay Kay, stn 40, holotype, MNHNCL-200734, L=41.3 mm. A. Exterior of left valve. B. Exterior of right valve. C. Interior of left valve. D. Interior of right valve. E. Left hinge plate. F. Right hinge plate. G. Dorsal view of left valve. H. Anterior view.

Calyptogena gallardoiSellanes & Krylova, 2005: 970, figs 1–3.

Type material: MNHNCL-200734 (holotype, 2 dry valves); MNHNCL-200735 (paratypes, 4 articulated valves); MNHNCL-200736 (paratypes, 13 separated valves); ZMMU-Ld2999 (2 articulated and 2 separated valves). Type locality: 72 km north-west off the Bay of Concepción, 36°22.21′S, 73°42.83′W, 760 m, 2 June 2004 (RV Kay Kay, Stn 40).

Material examined: Type material.

Diagnosis: Calyptogena species with L to 45 mm, stout, elongate-elliptical, H/L=0.58–0.63, W/L=0.18–0.21, ventral margin slightly convex, escutcheon not very deep, umbo situated in anterior 27–31% of valve, prosogyrate slightly enrolled beaks, moderate nymph, fibrous layer of ligament occupying 26–34% of valve length and 62–71% of posterior lamellar layer, 4b-tooth occupying a little more than half of nymph length.

Description: Shell medium-sized, L to 45 mm, stout, elongate-elliptical in outline, equivalve. Periostracum brownish, nearly absent except meagre remnant present mainly on periphery of ventral margin. Sculpture of irregular growth lines and wrinkles. Escutcheon moderate, sometimes lunular incision developed. Inequilateral, umbo situated at 27–31% from anterior end of valve. Umbones prosogyrate, not very low. Beaks slightly enrolled, not touching each other.

Antero-dorsal margin nearly straight or slightly convex, anterior margin broadly rounded, ventral margin slightly convex, posterior margin from tapering to rounded and postero-dorsal margin nearly straight or slightly convex. Pallial line somewhat broad, not impressed. Anterior adductor scar ovately conic, posterior margin of anterior adductor scar slightly impressed to rear. Anterior pedal retractor scar shallow. Posterior adductor scar slightly impressed anteriorly, square-rounded, fused to posterior pedal retractor scar. Nymph not strong, with sloping posterior end. Along posterior part of base of nymph, there is slight depression. Fibrous layer of ligament attaching to nymph comprises 62–71% of posterior lamellar layer and 26–34% of valve length. Dentition of right valve: ventral cardinal (1) stout, shelf-like, radiates obliquely anteriorwards; 3a-ramus lamellate, almost parallel to anterior-dorsal shell margin, fused in its proximal part with anterior edge of 3b-ramus; 3b-ramus broad, with slightly concave top surface and slightly rising anterior and posterior edges; posterior lateral obsolete, occupying a little more than half of nymph length. Dentition of left valve: 2a-ramus lamellate, parallel to anterior-dorsal shell margin, fused in its proximal part with the anterior edge of 2b-ramus; 2b-ramus broad, radiates ventralwards; 4b-tooth elongate, low, occupying a little more than half of nymph length.

Variation: The shape of the shell can be more or less elliptical. The nymph varies from weak to moderate; the depression along the posterior part of the base of the nymph can be more developed.

Remarks: Based on the elongate-elliptical shape of the shell, C. gallardoi is most similar to C. pacifica, C. goffrediae n. sp. and C. starobogatovi n. sp. From C. pacifica the present species differs by a less developed escutcheon, weaker nymph with sloping posterior margin, and less developed 4b-tooth in the left valve and posterior nymphal ridge in the right valve. Calyptogena goffrediae n. sp. differs from C. gallardoi by having a shallower escutcheon, more curved beaks and a more expanded antero-dorsal shell region. From C. starobogatovi the present species differs by the umbo, placed more anteriorly and by the absence of a glossy periostracum.

Distribution: 72 km north-west off the Bay of Concepción, south-central Chile East Pacific Ocean (36°22.21′S 73°42.83′W), 760 m.

Calyptogena goffrediae new species

(Figs 15, 16)

Figure 15.

Calyptogena goffrediae n. sp., RV Sonne, stn 1, holotype, SMF 327534, L=38.1 mm. A. Exterior of left valve. B. Exterior of right valve. C. Interior of left valve. D. Interior of right valve. E. Left hinge plate. F. Right hinge plate. G. Dorsal view. H. Anterior view.

Figure 15.

Calyptogena goffrediae n. sp., RV Sonne, stn 1, holotype, SMF 327534, L=38.1 mm. A. Exterior of left valve. B. Exterior of right valve. C. Interior of left valve. D. Interior of right valve. E. Left hinge plate. F. Right hinge plate. G. Dorsal view. H. Anterior view.

Figure 16.

Calyptogena goffrediae n. sp., RV Sonne, stn 1. A–D. Paratype, SMF 327535, L – 36.4 mm. A. Exterior of left valve. B. Exterior of right valve. C. Interior of left valve. D. Interior of right valve. E–G. Paratype, SMF 327536, L=24.6 mm. E. Exterior of left valve. F. Exterior of right valve. G. Interior of right valve. H–L. Paratype, L=20.6 mm. H. Exterior of left valve. I. Exterior of right valve. J. Interior of left valve. K. Interior of right valve. L. Anterior view; arrow indicates lunular incision.

Figure 16.

Calyptogena goffrediae n. sp., RV Sonne, stn 1. A–D. Paratype, SMF 327535, L – 36.4 mm. A. Exterior of left valve. B. Exterior of right valve. C. Interior of left valve. D. Interior of right valve. E–G. Paratype, SMF 327536, L=24.6 mm. E. Exterior of left valve. F. Exterior of right valve. G. Interior of right valve. H–L. Paratype, L=20.6 mm. H. Exterior of left valve. I. Exterior of right valve. J. Interior of left valve. K. Interior of right valve. L. Anterior view; arrow indicates lunular incision.

Type material: SMF 327534 (holotype, dry valves); SMF 327535 (paratype, dry valves); SMF 327536 (paratype, dry valves); SMF 327537 (2 paratypes, dry valves); ZMMU Ld-3000 (4 paratypes, dry valves). Type locality: Paita, Peru, East Pacific Ocean (5°35.06′S, 81°38.53′W), 3136 m.

Material examined: RV Sonne, Cruise 146, Stn 1, TVG; 5°35.06′S, 81°38.53′ W, 3136 m, 17 March 2000, 10 specimens without soft parts (including holotype and 8 paratypes).

Diagnosis: Calyptogena-species with L to 38.1 mm, moderately stout, elongate-elliptical, H/L=0.56–0.67, W/L=0.17–0.22, ventral margin slightly convex with nearly straight region along ventral midpoint, with adherent grayish-brownish periostracum becoming more wrinkled towards periphery, shallow escutcheon, indistinct lunule, umbo situated in anterior 29–32% of valve length, prosogyrate enrolled beaks, weak nymph, fibrous layer of ligament occupying 17–30% of valve length and 47–75% of posterior lamellar layer (Table 7).

Table 7.

Measurements of right valves of Calyptogena goffrediae.

 L (mm) H (mm) W (mm) F (mm) N (mm) H/L W/L F/N F/L N/L Um (%) 
Holotype, SMF 327534 38.1 21.4 6.5 8.8 13.5 0.56 0.17 0.65 0.23 0.35 29 
Paratype 1, SMF 327537 38.1 23.0 6.8 10.4 14.1 0.60 0.18 0.74 0.27 0.37 30 
Paratype 2, ZMMU Ld-3000 36.5 23.1 7.5 10.9 15.6 0.63 0.21 0.70 0.30 0.43 31 
Paratype 3, SMF 327535 36.4 22.0 6.4 8.5 12.3 0.60 0.18 0.69 0.23 0.34 29 
Paratype 4, ZMMU Ld-3000 36.2 23.4 7.8 10.5 14.0 0.65 0.22 0.75 0.29 0.39 30 
Paratype 5, ZMMU Ld-3000 34.7 21.4 7.1 9.0 13.5 0.62 0.20 0.67 0.26 0.39 30 
Paratype 6, SMF 327537 28.5 18.8 6.3 6.8 10.0 0.66 0.22 0.68 0.24 0.35 32 
Paratype 7, SMF 327536 24.6 15.7 5.4 5.3 8.2 0.64 0.22 0.65 0.22 0.33 32 
Paratype 8, ZMMU Ld-3000 22.3 14.8 4.4 4.5 7.8 0.66 0.20 0.58 0.20 0.35 32 
 20.6 13.8 3.9 3.5 7.5 0.67 0.19 0.47 0.17 0.36 32 
 L (mm) H (mm) W (mm) F (mm) N (mm) H/L W/L F/N F/L N/L Um (%) 
Holotype, SMF 327534 38.1 21.4 6.5 8.8 13.5 0.56 0.17 0.65 0.23 0.35 29 
Paratype 1, SMF 327537 38.1 23.0 6.8 10.4 14.1 0.60 0.18 0.74 0.27 0.37 30 
Paratype 2, ZMMU Ld-3000 36.5 23.1 7.5 10.9 15.6 0.63 0.21 0.70 0.30 0.43 31 
Paratype 3, SMF 327535 36.4 22.0 6.4 8.5 12.3 0.60 0.18 0.69 0.23 0.34 29 
Paratype 4, ZMMU Ld-3000 36.2 23.4 7.8 10.5 14.0 0.65 0.22 0.75 0.29 0.39 30 
Paratype 5, ZMMU Ld-3000 34.7 21.4 7.1 9.0 13.5 0.62 0.20 0.67 0.26 0.39 30 
Paratype 6, SMF 327537 28.5 18.8 6.3 6.8 10.0 0.66 0.22 0.68 0.24 0.35 32 
Paratype 7, SMF 327536 24.6 15.7 5.4 5.3 8.2 0.64 0.22 0.65 0.22 0.33 32 
Paratype 8, ZMMU Ld-3000 22.3 14.8 4.4 4.5 7.8 0.66 0.20 0.58 0.20 0.35 32 
 20.6 13.8 3.9 3.5 7.5 0.67 0.19 0.47 0.17 0.36 32 

Description of holotype: Shell moderately solid, elongate-elliptical in outline, H/L=0.56, equivalve. Periostracum adherent, translucent, thin, grayish. Sculpture of irregular growth lines and wrinkles. Escutcheon shallow, lunule indistinct. Inequilateral, umbo situated at anterior 29% of valve length. Umbones prosogyrate, not very low. Beaks enrolled, nearly touching each other. Antero-dorsal margin slightly convex, anterior margin rounded-truncated, ventral margin slightly convex, posterior margin rounded, posterodorsal margin straight. Pallial line not impressed, pallial sinus absent. Anterior adductor scar irregularly oval, posterior margin of anterior adductor scar slightly impressed to rear. Anterior pedal retractor scar shallow. Posterior adductor scar not impressed, pear-shaped, fused to posterior pedal retractor scar. Nymph weak, with sloping posterior end, occupies 23% of valve length. Along all the base of nymph, there is very slight depression. Fibrous layer of ligament, attaching to nymph, is 65% of posterior lamellar layer. Dentition of right valve: ventral cardinal (1) stout, shelf-like, radiates obliquely anterior-wards; 3a-ramus lamellate, short, almost parallel to anterior-dorsal shell margin, fused in its proximal part with anterior edge of 3b-ramus; 3b-ramus broad, with slightly concave top surface and slightly rising anterior and posterior edges; posterior nymphal ridge very low. Dentition of left valve: 2a-ramus lamellate, parallel to anterior-dorsal shell margin, fused in its proximal part with anterior edge of 2b-ramus; 2b-ramus broad, radiates ventralwards; 4b-tooth elongate, low, weak, occupying less than half of nymph.

Variation: Variations can be seen in the shape of valves and in the dental configuration. Shell shape can be more or less elongate and the outlines of the anterior and posterior margins can vary from rounded to subtruncate. Younger specimens usually have more rounded anterior margins and truncate posterior margins. The ventral margin can be more or less convex. The lengths of fibrous layers vary; more elongate fibrous layers of the ligament are found in larger specimens. In the right valve, the ventral cardinal (1) can range from thin and shelf-like to stout and wedge-like; the 3a-ramus can be nearly fused with the antero-dorsal margin, and therefore be indistinct; the right posterior nymphal ridge can be reduced.

Remarks: The elongate-elliptical shape of C. goffrediae n. sp. is most similar to C. pacifica, C. gallardoi and C. starobogatovi n. sp., from all of which it differs by the enrolled beaks, adherent periostracum and more expanded anterior-doral shell region (Table 11). Additionally, from C. pacifica the present species differs by having a thinner shell, a shallower escutcheon and a weaker nymph, and from C. starobogatovi by the more anteriorly placed umbo.

Distribution: Paita, Peru, East Pacific (5°35.06′S, 81°38.53′W), 3136 m.

Etymology: Named for Shana Goffredi (California Institute of Technology, USA) who has made a great contribution to the biology of symbiotrophic bivalves.

Calyptogena starobogatovi new species

(Figs 17, 18)

Figure 17.

Calyptogena starobogatovi n. sp. RV Akademik Mstislav Keldysh, stn 1505, holotype, ZMMU Ld-3001, L=33.8 mm. A. Exterior of left valve. B. Exterior of right valve. C. Interior of left valve. D. Interior of right valve. E. Left hinge plate. F. Right hinge plate. G. Dorsal view. H. Anterior view.

Figure 17.

Calyptogena starobogatovi n. sp. RV Akademik Mstislav Keldysh, stn 1505, holotype, ZMMU Ld-3001, L=33.8 mm. A. Exterior of left valve. B. Exterior of right valve. C. Interior of left valve. D. Interior of right valve. E. Left hinge plate. F. Right hinge plate. G. Dorsal view. H. Anterior view.

Figure 18.

Calyptogena starobogatovi n. sp., RV Akademik Mstislav Keldysh, stn 1505. A–F. Paratype, SMF 327538, L=41.4 mm. A. Exterior of left valve. B. Exterior of right valve. C. Interior of left valve. D. Interior of right valve. E. Left hinge plate. F. Right hinge plate. G–L. L=36.4 mm. G. Exterior of left valve. H. Exterior of right valve. I. Interior of left valve. J. Interior of right valve. K. Left hinge plate. L. Right hinge plate.

Figure 18.

Calyptogena starobogatovi n. sp., RV Akademik Mstislav Keldysh, stn 1505. A–F. Paratype, SMF 327538, L=41.4 mm. A. Exterior of left valve. B. Exterior of right valve. C. Interior of left valve. D. Interior of right valve. E. Left hinge plate. F. Right hinge plate. G–L. L=36.4 mm. G. Exterior of left valve. H. Exterior of right valve. I. Interior of left valve. J. Interior of right valve. K. Left hinge plate. L. Right hinge plate.

Type material: ZMMU Ld-3001 (holotype, with soft parts); ZMMU Ld-3002 (2 paratypes, dry valves); SMF 327538 (paratype, dry valves); SMF 327539 (3 paratypes, dry valves). Type locality: Axial Seamount, Juan de Fuca Ridge, East Pacific Ocean (45°55.63′N, 130°01.81′W), 1540 m.

Material examined: RV Akademik Mstislav Keldysh, 12th cruise, stn 1505, ‘Pisces XI’, 45°55′N, 130°01′W, 1540 m, 26 September 1986, 36 specimens (including holotype and 6 paratypes).

Diagnosis: Calyptogena species with L to 42 mm, moderately stout, elongate-elliptical, H/L=0.58–0.66, W/L=0.16–0.21, with slightly convex ventral margin, adherent glossy yellowish periostracum, shallow escutcheon, low umbo situated in anterior 32–39% of valve length, usually corroded nearly orthogyrate beaks, nymph moderately strong but short, fibrous layer of ligament occupying 12–24% of valve length and 44–59% of posterior lamellar layer (Table 8).

Table 8.

Measurements of right valves of Calyptogena starobogatovi.

 L (mm) H (mm) W (mm) F (mm) N (mm) H/L W/L F/N F/L N/L Um (%) 
Holotype, ZMMU Ld-3001 33.8 19.9 5.6 6.6 13.0 0.59 0.17 0.51 0.20 0.38 37 
Paratype 1, SMF 327538 41.4 24.1 7.2 9.2 15.7 0.58 0.17 0.59 0.22 0.38 32 
Paratype 2, ZMMU Ld-3002 39.3 25.4 6.9 9.0 17.3 0.65 0.18 0.52 0.23 0.44 35 
 37.4 24.0 6.7 8.6 15.0 0.64 0.18 0.57 0.23 0.40 37 
Paratype 3, ZMMU Ld-3002 33.2 21.6 7.0 7.7 13.2 0.65 0.21 0.58 0.23 0.40 35 
Paratype 4, SMF 327539 32.4 19.3 6.1 7.1 13.4 0.60 0.19 0.53 0.22 0.41 34 
 30.5 18.5 5.7 7.2 12.6 0.61 0.19 0.57 0.24 0.41 30 
Paratype 5, SMF 327539 30.5 17.9 5.5 6.6 11.4 0.59 0.18 0.58 0.22 0.37 36 
 26.8 15.5 4.4 5.1 10.1 0.58 0.16 0.50 0.19 0.38 35 
 26.2 15.1 5.0 4.9 9.8 0.58 0.19 0.53 0.19 0.37 35 
Paratype 6, SMF 327539 14.0 9.3 2.9 1.7 3.9 0.66 0.21 0.44 0.12 0.28 39 
 L (mm) H (mm) W (mm) F (mm) N (mm) H/L W/L F/N F/L N/L Um (%) 
Holotype, ZMMU Ld-3001 33.8 19.9 5.6 6.6 13.0 0.59 0.17 0.51 0.20 0.38 37 
Paratype 1, SMF 327538 41.4 24.1 7.2 9.2 15.7 0.58 0.17 0.59 0.22 0.38 32 
Paratype 2, ZMMU Ld-3002 39.3 25.4 6.9 9.0 17.3 0.65 0.18 0.52 0.23 0.44 35 
 37.4 24.0 6.7 8.6 15.0 0.64 0.18 0.57 0.23 0.40 37 
Paratype 3, ZMMU Ld-3002 33.2 21.6 7.0 7.7 13.2 0.65 0.21 0.58 0.23 0.40 35 
Paratype 4, SMF 327539 32.4 19.3 6.1 7.1 13.4 0.60 0.19 0.53 0.22 0.41 34 
 30.5 18.5 5.7 7.2 12.6 0.61 0.19 0.57 0.24 0.41 30 
Paratype 5, SMF 327539 30.5 17.9 5.5 6.6 11.4 0.59 0.18 0.58 0.22 0.37 36 
 26.8 15.5 4.4 5.1 10.1 0.58 0.16 0.50 0.19 0.38 35 
 26.2 15.1 5.0 4.9 9.8 0.58 0.19 0.53 0.19 0.37 35 
Paratype 6, SMF 327539 14.0 9.3 2.9 1.7 3.9 0.66 0.21 0.44 0.12 0.28 39 

Description of holotype: Shell subsolid, elongate-elliptical in outline, H/L=0.59, equivalve. Periostracum adherent, thin, glossy, yellowish, pinkish in posterior part and at periphery, with thin radiating striation, smooth in region of umbo, becoming wrinkled in marginal region and with short, concentric, up-standing lamellae developed mostly at periphery. Sculpture consisting of irregular concentric growth lines and inconspicuous lirae radiating from umbo to posterior margin. Escutcheon shallow. Inequilateral, umbo situated in anterior 37% of valve length. Umbo highly corroded and therefore very low. Anterior margin rounded, ventral margin convex, posterior margin rounded subtruncate with postero-dorsal obtuse angle and posterodorsal margin straight. Pallial line not impressed. Anterior adductor scar and posterior adductor slightly impressed. Anterior pedal retractor scar shallow. Nymph moderately strong, short, occupies 20% of valve length. Fibrous layer of ligament is 51% of posterior lamellar layer. Dentition of right valve: ventral cardinal (1) stout, shelf-like, radiates obliquely anteriorwards; 3a-ramus lamellate, thin, nearly twice shorter than (1), subparallel to anterior-dorsal shell margin, depressed in its proximal part and fused with anterior edge of 3b-ramus; 3b-ramus broad, with slightly elevated narrow anterior and posterior edges, posterior edge lower and parallel to posterior nymphal ridge, anterior edge radiates anteriorwards; posteral nymphal ridge low, elongate, occupies nearly all the length of nymph, parallel to posterior-dorsal margin, more developed in distal part. Dentition of left valve: 2a-ramus lamellate, thin, radiates anteriorwards, fused in its proximal part with 2b-ramus; 2b-ramus broad, with more developed proximal posterior part, radiates ventralwards; 4b-tooth elongate, lamellate in its proximal part and parallel posterior-dorsal shell margin, occupying more than half of nymph.

Anatomy: All features of genus.

Variation: Variations can be shown in the colour and shape of shells, in details of sculpture and of the hinge line. Shell colour varies from nearly white through yellowish to pinkish. The number of lirae radiating from the umbo to the posterior margin also varies and they can be absent. As a result of corrosion, the beaks can be nearly absent. If not corroded, the beaks are placed very closely and touch each other. The outline of the shell can be more or less elongate. The position of the umbo, the length of the nymph and the length of the fibrous layer of the ligament vary remarkably. Variations in the dentition: the right cardinal 3a can be nearly fused with the antero-dorsal margin and therefore may be indistinct; the length of the right posterior nymphal ridge can vary from 3/4 length of nymph to full length; sometimes it can be reduced. Sometimes the hinge margin can be highly corroded. Allometric changes are evident in the slightly more elongate ligament and more truncate posterior margin of larger specimens.

Remarks: The elongate-elliptical shell shape of the C. starobogatovi n. sp. is close to those of C. pacifica, C. goffrediae n. sp. and C. gallardoi (Table 11). From all these species C. starobogatovi n. sp. differs by the presence of a glossy, smoother periostracum, a lower umbo placed more medially and the more expanded posterior portion of shell. In addition, from C. pacifica the present species differs by the thinner shell, shallower escutcheon and shorter fibrous ligament layer.

Distribution: Eastern Pacific in the region of Juan de Fuca Ridge, 1540 m.

Etymology. Named after the late Ya. I. Starobogatov, outstanding Russian zoologist, who began to study this material and recognized a new species.

Calyptogena makranensis new species

(Figs 19, 20)

Figure 19.

Calyptogena makranensis n. sp., RV Sonne, stn 322, holotype, SMF 327540, L=62.8 mm. A. Exterior of left valve. B. Exterior of right valve. C. Interior of left valve. D. Interior of right valve. E. Left hinge plate. F. Right hinge plate. G. Dorsal view. H. Anterior view.

Figure 19.

Calyptogena makranensis n. sp., RV Sonne, stn 322, holotype, SMF 327540, L=62.8 mm. A. Exterior of left valve. B. Exterior of right valve. C. Interior of left valve. D. Interior of right valve. E. Left hinge plate. F. Right hinge plate. G. Dorsal view. H. Anterior view.

Figure 20.

Calyptogena makranensis n. sp., RV Sonne, stn 322. A–D. Paratype, SMF 327541, L=66.5 mm. A. Exterior of left valve. B. Exterior of right valve. C. Interior of left valve. D. Interior of right valve. E–G. Paratype, SMF 327542, L=33.7 mm. E. Exterior of left valve. F. Interior of left valve. G. Interior of right valve.

Figure 20.

Calyptogena makranensis n. sp., RV Sonne, stn 322. A–D. Paratype, SMF 327541, L=66.5 mm. A. Exterior of left valve. B. Exterior of right valve. C. Interior of left valve. D. Interior of right valve. E–G. Paratype, SMF 327542, L=33.7 mm. E. Exterior of left valve. F. Interior of left valve. G. Interior of right valve.

Type material: SMF 327540 (holotype, dry valves); SMF 327541 (paratype, dry valves); SMF 327542 (paratype, dry valves); SMF 327543 (paratype, dry valves); ZMMU Ld-3003 (3 paratypes, dry valves). Type locality: Makran continental margin off Pakistan, Indian Ocean (24°32.94′N, 64°15.70′E), 2336 m.

Material examined: RV Sonne, Cruise 130, Stn 320, TVG, 24°33.09′N, 64°15.79′E, 2215 m, 28 April 1998, 75 intact and 54 broken vs; Stn 322, TVG, 24°32.94′N, 64°15.70′E, 2336 m, 28 April 1998, 132 intact and 9 broken vs (including holotype and six paratypes); Stn 330, TVG, 24°33.00′N, 64°15.64′E, 2334 m, 01. Mai 1998, 2 spms, 54 vs.

Diagnosis: Calyptogena species with L to 87 mm, stout, elongate, H/L=0.45–0.56, W/L=0.13–0.18, with nearly straight ventral margin, with glossy, smooth, brownish periostracum becoming wrinkled at periphery, moderate escutcheon, limited by sharp ridge, very low umbo situated in anterior 31–35% of valve length, weakly prosogyrate beaks, nymph strong, fibrous layer of ligament occupying 28–43% of valve length and 64–80% of posterior lamellar layer, 4b-tooth occupying nearly half of nymph length (Table 9).

Table 9.

Measurements of right valves of Calyptogena makranensis.

 L (mm) H (mm) W (mm) F (mm) N (mm) H/L W/L F/N F/L N/L Um (%) 
Holotype, SMF327540 62.8 31.2 8.3 20.3 26.3 0.50 0.13 0.77 0.32 0.42 34 
Paratype 1, ZMMULd-33003 86.4 41.3 13.1 29.0 39.3 0.48 0.15 0.74 0.34 0.45 31 
Paratype 2, SMF 327543 76.5 34.3 10.2 29.0 36.1 0.45 0.13 0.80 0.38 0.47 32 
Paratype 3, ZMMU Ld-3003 67.2 34.4 10.2 29.0 36.2 0.51 0.15 0.80 0.43 0.54 34 
Paratype 4, SMF 327541 66.5 32.6 10.0 22.3 30.4 0.49 0.15 0.73 0.34 0.46 31 
Paratype 5, ZMMU Ld-3003 57.1 26.2 7.5 17.7 26.4 0.46 0.13 0.67 0.31 0.46 31 
Paratype 6, SMF 327542 33.7 18.8 5.5 9.4 14.6 0.56 0.16 0.64 0.28 0.43 35 
RV Sonne 130, stn 320 52.1 26.2 7.4 15.4 23.1 0.50 0.14 0.67 0.30 0.44 33 
RV Sonne, stn 330 82.7 44.2 15.0 28.1 38.3 0.53 0.18 0.73 0.34 0.46 31 
 81.2 41.6 13.4 25.3 38.6 0.51 0.17 0.66 0.31 0.48 31 
 L (mm) H (mm) W (mm) F (mm) N (mm) H/L W/L F/N F/L N/L Um (%) 
Holotype, SMF327540 62.8 31.2 8.3 20.3 26.3 0.50 0.13 0.77 0.32 0.42 34 
Paratype 1, ZMMULd-33003 86.4 41.3 13.1 29.0 39.3 0.48 0.15 0.74 0.34 0.45 31 
Paratype 2, SMF 327543 76.5 34.3 10.2 29.0 36.1 0.45 0.13 0.80 0.38 0.47 32 
Paratype 3, ZMMU Ld-3003 67.2 34.4 10.2 29.0 36.2 0.51 0.15 0.80 0.43 0.54 34 
Paratype 4, SMF 327541 66.5 32.6 10.0 22.3 30.4 0.49 0.15 0.73 0.34 0.46 31 
Paratype 5, ZMMU Ld-3003 57.1 26.2 7.5 17.7 26.4 0.46 0.13 0.67 0.31 0.46 31 
Paratype 6, SMF 327542 33.7 18.8 5.5 9.4 14.6 0.56 0.16 0.64 0.28 0.43 35 
RV Sonne 130, stn 320 52.1 26.2 7.4 15.4 23.1 0.50 0.14 0.67 0.30 0.44 33 
RV Sonne, stn 330 82.7 44.2 15.0 28.1 38.3 0.53 0.18 0.73 0.34 0.46 31 
 81.2 41.6 13.4 25.3 38.6 0.51 0.17 0.66 0.31 0.48 31 

Description of holotype: Shell stout; elongate in outline, H/L=0.50, equivalve. Valves more flattened towards dorsal margin. Periostracum eroded in the umbonal region, thin, glossy, yellow-brownish and darker and wrinkled towards periphery. Sculpture of growth lines and low irregular concentric ridges. Escutcheon moderate, limited by sharp ridge; lunule narrow and long, limited by slightly raised ridges. Inequilateral, umbo situated at 34% of length from anterior end of valve. Umbones prosogyrate low. Beaks slightly enrolled and nearly touching each other. Anterior-dorsal margin straight, anterior and posterior margins rounded, ventral margin nearly straight, posterior-dorsal margin straight with posterior obtuse angle. Pallial line distinct, slightly impressed. Anterior adductor scar irregularly oval, slightly impressed to rear. Anterior pedal retractor scar shallowly impressed, not fused with anterior adductor scar, but connected to it by narrow line. Posterior adductor scar clearly visible but not impressed, as wide as high, pear-shaped, fused to posterior pedal retractor scar. Nymph strong, with sloping posterior end, occupies 32% of valve length. Fibrous layer of ligament, which attaches to nymph, is 77% of posterior lamellar layer. Dentition of right valve: ventral cardinal (1) thin, shelf-shaped, radiates obliquely anteriorwards; 3a-ramus thin, lamellate, parallel to anterior-dorsal shell margin, fused in its low proximal part with anterior edge of 3b-ramus; 3b-ramus broad, low, with slightly elevated anterior and posterior edges and concave top surface, anterior edge usually radiates ventrally, posterior edge parallel to posterior nymphal ridge; posterior nymphal ridge elongate, occupying nearly half of nymph. Dentition of left valve: 2a-ramus shelf-like, sub-parallel to anterior-dorsal shell margin, fused in its proximal part with proximal part of 2b-ramus; 2b-ramus thicker and shorter than 2b, radiates ventralwards; 4b-tooth elongate, occupying nearly half of nymph, sub-parallel to posterior-dorsal shell margin.

Anatomy: All features of genus.

Variation: The shape of the shell can be more or less elongate. The length of the fibrous layer of the ligament varies. The postero-dorsal margin can be convex, sloping posteriorly, so that the posterior margin is acute. The lunular region may not be impressed at all. In the right valve the ventral cardinal (1) can range from thin and shelf-like to stout and wedge-like; the 3a-ramus can be nearly fused with the antero-dorsal margin; the anterior and posterior edges of the 3b-ramus may not be parallel to each other.

Remarks: Based on the elongate shape of the shell, C. makranensis n. sp. is most similar to C. rectimargo, C. fausta and C. costaricana n. sp. (Table 11). From C. rectimargo and C. fausta it differs by the less prominent umbo, placed more medially. From C. fausta the new species differs also by the shorter and not split posterior nymphal ridge in the right valve. It differs from C. costaricana by the relatively longer right posterior nymphal ridge, a longer nymph, longer posterior lamellar ligament and the deeper escutcheon that is limited by a sharp ridge.

There are few records of vesicomyids from the Indian Ocean; three species were described by Smith (1904, 1906) from material obtained by R/V Investigator off the coast of India and Ceylon, and two species were collected recently from the eastern part of the Indian ocean, off Sunda Strait (Kojima et al., 2004). The species described by Smith are: Vesicomya indicaSmith, 1904, from off Travancore coast, 666 m and off Andamans, 749 m; V. cretaceaSmith, 1906, from off Burma, 754 m and off Ceylon, 2007 m; and V. brevisSmith, 1906 from the Laccadive Sea, 546–666 m. All of these species are closely related to each other and Boss (1970) supposed that these species together with V. compressaPrashad, 1932 may prove to be a single Indo-Pacific species. These species differ from Calyptogena by their subovate shell shape, well-developed lunule, presence of a pallial sinus that is weakly developed, and by the absence of right posterior nymphal ridge. Similar to Calyptogena, however, these species have a well-developed escutcheon.

Both species collected from off the Sunda Strait, 2100 m (Kojima et al., 2004) were studied only by molecular methods. One of these species formed a well-supported group with V. crenulomarginataOkutani, Kojima & Iwasaki (2002), described from the Nankai Trough, and the other species is closely related to Calyptogena (Archivesica) similarisOkutani, Kojima & Ashi (1997), also known from the Nankai Trough. From V. crenulomarginata our species differs by the more elongated shell, absence of well-developed lunule and pallial sinus and by different hinge margin. From ‘C. (Archivesica)similaris, C. makranensis is distinguished by the absence of a pallial sinus, a quite different hinge margin without a subumbonal pit and with a right posterior nymphal ridge, and also by presence of only one demibranch. Consequently, C. makranensis n. sp. is the first record of the genus Calyptogena in the Indian Ocean.

Distribution: Makran continental margin off Pakistan, northwestern Indian Ocean, 2213–2336 m.

Etymology: Named after type locality.

Calyptogena costaricana new species

(Figs 21, 22)

Figure 21.

Calyptogena costaricana n. sp., RV Meteor, stn 123, holotype, SMF 327544, L=50.8 mm. A. Exterior of left valve. B. Exterior of right valve. C. Interior of left valve. D. Interior of right valve. E. Left hinge plate. F. Right hinge plate. G. Dorsal view. H. Anterior view.

Figure 21.

Calyptogena costaricana n. sp., RV Meteor, stn 123, holotype, SMF 327544, L=50.8 mm. A. Exterior of left valve. B. Exterior of right valve. C. Interior of left valve. D. Interior of right valve. E. Left hinge plate. F. Right hinge plate. G. Dorsal view. H. Anterior view.

Figure 22.

Calyptogena costaricana n. sp., RV Meteor, stn 134. A–F. Paratype, ZMMU Ld-3004, L=52.0 mm. A. Exterior of left valve. B. Exterior of right valve. C. Interior of left valve. D. Interior of right valve. E. Left hinge plate. F. Right hinge plate. G–L. Paratype, ZMMU Ld-3004, L=38.4 mm. G. Exterior of left valve. H. Exterior of right valve. I. Interior of left valve. J. Interior of right valve. K. Left hinge plate. L. Right hinge plate.

Figure 22.

Calyptogena costaricana n. sp., RV Meteor, stn 134. A–F. Paratype, ZMMU Ld-3004, L=52.0 mm. A. Exterior of left valve. B. Exterior of right valve. C. Interior of left valve. D. Interior of right valve. E. Left hinge plate. F. Right hinge plate. G–L. Paratype, ZMMU Ld-3004, L=38.4 mm. G. Exterior of left valve. H. Exterior of right valve. I. Interior of left valve. J. Interior of right valve. K. Left hinge plate. L. Right hinge plate.

Type material: SMF 327544 (holotype, with soft parts); SMF 327545 (paratype, with soft parts; Stn 123); SMF 327546 (paratype, dry valves; Stn 134); ZMMU Ld-3004 (3 paratypes, with soft parts; 1 paratype, dry valves; Stn 134). Type locality: Mound 10, off Costa Rica, East Pacific Ocean (10°00.43′N, 86°11.45′W), 2263 m.

Material examined: RV Meteor, Cruise 54/3, Stn 123, TV-MUC, 10°00.43′N, 86°11.45′W, 2263 m, 14 September 2002, 2 spms (including holotype and paratype); Stn 134, TVG, 10°00.52′N, 86°11.41′W, 2258 m, 16 September 2002, 3 spms and 4 vs (paratypes).

Diagnosis: Calyptogena species with L to 52 mm, stout, elongate, H/L=0.50–0.59, W/L=0.16–0.21, with nearly straight ventral margin, dehiscent glossy periostracum becoming strongly wrinkled to periphery, shallow escutcheon, low umbo situated in anterior 31–35% of valve length, prosogyrate beaks, moderate nymph, fibrous layer of ligament occupying 28–33% of valve length and 66–87% of posterior lamellar layer, 4b-tooth occupying less than a half of nymph length, right posterior nymphal ridge sometimes reduced (Table 10).

Table 10.

Measurements of right valves of Calyptogena costaricana.

 L (mm) H (mm) W (mm) F (mm) N (mm) H/L W/L F/N F/L N/L Um (%) 
RV Meteor, stn 123            
 Holotype, SMF 327544 50.8 26.8 8.7 14.8 21.1 0.53 0.17 0.70 0.29 0.42 33 
 Paratype 1, SMF 327545 33.2 19.5 6.9 9.4 14.3 0.59 0.21 0.66 0.28 0.43 33 
RV Meteor, stn 134            
 Paratype 2, ZMMU Ld-3004 52.0 26.2 8.5 16.6 21.6 0.50 0.16 0.77 0.32 0.42 31 
 Paratype 3, ZMMU Ld-3004 40.8 21.1 6.8 12.7 16.5 0.52 0.17 0.77 0.31 0.40 33 
 Paratype 4, ZMMU Ld-3004 38.4 19.8 6.8 12.2 16.6 0.52 0.18 0.73 0.32 0.43 35 
 Paratype 5, SMF 327546 37.1 19.0 6.0 12.2 14.0 0.51 0.16 0.87 0.33 0.38 32 
 Paratype 6, ZMMU Ld-3004 37.0 19.0 6.3 11.8 16.5 0.51 0.17 0.72 0.32 0.45 33 
 L (mm) H (mm) W (mm) F (mm) N (mm) H/L W/L F/N F/L N/L Um (%) 
RV Meteor, stn 123            
 Holotype, SMF 327544 50.8 26.8 8.7 14.8 21.1 0.53 0.17 0.70 0.29 0.42 33 
 Paratype 1, SMF 327545 33.2 19.5 6.9 9.4 14.3 0.59 0.21 0.66 0.28 0.43 33 
RV Meteor, stn 134            
 Paratype 2, ZMMU Ld-3004 52.0 26.2 8.5 16.6 21.6 0.50 0.16 0.77 0.32 0.42 31 
 Paratype 3, ZMMU Ld-3004 40.8 21.1 6.8 12.7 16.5 0.52 0.17 0.77 0.31 0.40 33 
 Paratype 4, ZMMU Ld-3004 38.4 19.8 6.8 12.2 16.6 0.52 0.18 0.73 0.32 0.43 35 
 Paratype 5, SMF 327546 37.1 19.0 6.0 12.2 14.0 0.51 0.16 0.87 0.33 0.38 32 
 Paratype 6, ZMMU Ld-3004 37.0 19.0 6.3 11.8 16.5 0.51 0.17 0.72 0.32 0.45 33 

Description of holotype: Shell stout, elongate in outline, H/L=0.53, equivalve. Periostracum eroded in umbonal region, dehiscent, thin, glossy, dirty-pinkish, wrinkled, with short concentric lamellae perpendicular to surface, developed mostly at periphery. Sculpture of growth lines and low irregular concentric ridges. Escutcheon shallow, lunule indistinct. Inequilateral, umbo situated at 33% from anterior end of valve. Umbones prosogyrate, low. Beaks slightly enrolled and nearly touching each other. Anterior-dorsal margin straight, anterior margin broadly rounded, ventral margin nearly straight, posterior margin acutely rounded and posterior-dorsal margin nearly straight. Pallial line distinct, slightly impressed. Anterior adductor scar irregularly oval, slightly impressed to rear. Anterior pedal retractor scar shallow. Posterior adductor scar clearly visible but not impressed, as wide as high, pear-shaped, fused to posterior pedal retractor scar. Nymph strong, with nearly abrupt posterior end, occupies 29% of valve length. Along distal part of the base of nymph there is very slight depression. Fibrous layer of ligament, which attaches to nymph, is 70% of posterior lamellar layer. Dentition of right valve: ventral cardinal (1) stout, shelf-shaped, radiates obliquely anteriorwards; 3a-ramus thin, lamellate, parallel to anterior-dorsal shell margin, fused in its low proximal part with anterior edge of 3b-ramus; 3b-ramus broad, low, with slightly raising anterior and posterior edges and concave top surface, anterior edge usually radiates ventrally, posterior edge radiates posteriorly; posterior nymphal ridge elongate, very low, occupying less than a half of nymph. Dentition of left valve: 2a-ramus thin, shelf-like, sub-parallel to anterior-dorsal shell margin, fused in its proximal part with proximal part of 2b-ramus; 2b-ramus thicker and shorter than 2a, radiates ventrally; 4b-tooth elongate, occupying less than a half of nymph, radiates posteriorwards.

Anatomy: All features of genus.

Variation: The shape of the shell can be more or less elongate. The postero-dorsal margin can be strongly convex, sloping posteriorly, and the ventral margin can be weakly concave. The location of the umbo and the length of the fibrous layers of the ligament also vary. The right posterior nymphal ridge can be reduced. The 4b-tooth can sometimes be slightly longer than half of the nymph. The colour of the periostacum of live-collected specimens is pinkish-brown, while the colour of dead valves is greyish-brown. The lunular region can sometimes be slightly impressed.

Remarks: The elongate shape of the shell of C. costaricana is most similar to C. rectimargo, C. fausta and C. makranensis (Table 11). From C. rectimargo and C. fausta, it differs by the more medially placed umbo. From C. fausta the new species differs also by the absence of a slit in the posterior nymphal ridge of the right valve. Calyptogena costaricana differs from C. makranensis by the shorter nymph, shorter right posterior nymphal ridge and shallower escutcheon.

Table 11.

Shell characteristics of recent Calyptogena species.

Species Maximum length (mm) Shell shape Escutcheon H/L Periostracum Position of umbo (%) Length of 4b-tooth 
C. pacifica 60 Elongate-elliptical Deep 0.55–0.65 Dehiscent 24–31 More than half nymph length 
C. starobogatovi n. sp. 42 Elongate-elliptical Shallow 0.58–0.66 Adherent 32–39 More than half nymph length 
C. goffrediae n. sp. 38.1 Elongate-elliptical Shallow 0.56–0.67 Adherent 29–32 Less than half nymph length 
C. valdiviae 73 Elongate-elliptical Deep 0.56–0.65 Adherent 30–36 Nearly half nymph length 
C. gallardoi 45 Elongate-elliptical Moderate 0.58–0.63 Dehiscent 27–31 Nearly half nymph length 
C. costaricana n. sp. 52 Elongate Shallow 0.50–0.59 Dehiscent 31–35 Less than half nymph length 
C. rectimargo 70 Elongate Moderate 0.45–0.56 Dehiscent 25–29 Nearly half nymph length 
C. fausta 70 Elongate Shallow 0.50 Adherent 26 More that half nymph length 
C. makranensis n. sp. 87 Elongate Moderate 0.45–0.56 Dehiscent 31–35 Nearly half nymph length 
Species Maximum length (mm) Shell shape Escutcheon H/L Periostracum Position of umbo (%) Length of 4b-tooth 
C. pacifica 60 Elongate-elliptical Deep 0.55–0.65 Dehiscent 24–31 More than half nymph length 
C. starobogatovi n. sp. 42 Elongate-elliptical Shallow 0.58–0.66 Adherent 32–39 More than half nymph length 
C. goffrediae n. sp. 38.1 Elongate-elliptical Shallow 0.56–0.67 Adherent 29–32 Less than half nymph length 
C. valdiviae 73 Elongate-elliptical Deep 0.56–0.65 Adherent 30–36 Nearly half nymph length 
C. gallardoi 45 Elongate-elliptical Moderate 0.58–0.63 Dehiscent 27–31 Nearly half nymph length 
C. costaricana n. sp. 52 Elongate Shallow 0.50–0.59 Dehiscent 31–35 Less than half nymph length 
C. rectimargo 70 Elongate Moderate 0.45–0.56 Dehiscent 25–29 Nearly half nymph length 
C. fausta 70 Elongate Shallow 0.50 Adherent 26 More that half nymph length 
C. makranensis n. sp. 87 Elongate Moderate 0.45–0.56 Dehiscent 31–35 Nearly half nymph length 

Calyptogena costaricana very much resembles in proportion and gross outline the fossil species C. panamensisOlsson (1942), from sandstones of the uppermost Miocene and lower Pliocene beds on the Burica Peninsula (boundary between Panama and Costa Rica). Comparison between these two species is difficult because the only specimen of C. panamensis showing the hinge has an obsolete tooth (Olsson, 1942), however C. panamensis differs from C. costaricana by more solid shell with broader hinge plate and shorter ligament.

Distribution: Off Costa Rica, eastern Pacific Ocean, 2258–2263 m.

Etymology: Named after the type locality.

DISCUSSION

Our study reveals that Calyptogena represents a compact group of species united by common adaptive strategies with similar morphological features. The most characteristic conchological and anatomical features of Calyptogena are: shell is usually medium-sized, up to 90 mm in length; elongate-elliptical or elongate shape of valves; presence of an escutcheon; presence of a broad posterior ramus (3b) of the right subumbonal cardinal tooth, as well as presence of a right posterior nymphal ridge and left elongated posterodorsal cardinal tooth (4b); absence of pallial sinus as a result of fusion of intersiphonal septal retractor in its distal part to the ventral surface of the posterior adductor and inserting on the shell immediately adjacent to it; absence of processes on inner vulva of inhalant siphon; ctenidia with inner demibranch only, with descending and ascending lamellae with interlamellar septa not divided into separate cylindrical tubes.

The taxonomic composition of the entire family Vesicomyidae is still uncertain. We have summarized the characteristic features of all genera that are currently referred to the family on the basis of the type species and species unequivocally closely related to the type species (Table 12). The large differences of Calyptogena from all other genera demand the separation of this group at the generic level. Several species were originally described as Calyptogena which we exclude from the genus. Table 13 lists those species and the main diagnostic characters which distinguish them from Calyptogena s.s. Further studies are needed in order to refine the generic allocation of these species.

Table 12.

Main characters of genera currently referred to the family Vesicomyidae.

 CalyptogenaDall, 1891 PhreagenaWoodring, 1938 EctenagenaWoodring, 1938 ArchivesicaDall, 1908 AkebiconchaKuroda, 1943 IsorropodonSturany, 1896 VesicomyaDall, 1886 PliocardiaWoodring, 1925 CallogoniaDall, 1889 WaisiuconchaBeets, 1942 HubertschenckiaTakeda, 1953 Pleurophopsisvan Winkle, 1919 
Type species Calyptogena pacificaDall, 1891 Phreagena lasiaWoodring, 1938 Calyptogena elongataDall, 1916 Vesicomya gigasDall, 1895 Akebiconcha kawamuraiKuroda, 1943 Isorropodon peplexumSturany, 1896 Callocardia atlanticaSmith, 1885 Anomalocardia bowdeniana Dall, 1903 Callocardia (Callogonia) leeanaDall, 1889 Waisiuconcha alberdinaeBeets, 1942 Tapes ezoensisYokoyama, 1890 Pleurophopsis unioidesvan Winkle, 1919 
Maximal shell size for genus (mm) 90 250 44 111 60 47 10 44 34 24 65 200 
Shell outline From elongate-elliptical to elongate Elongate Elongate From subovate to elongate-elliptical Elongate-elliptical From subcircular to subovate Subcircular Subovate Subovate Subcircular Subovate Elongate 
Tumidity Not inflated Not inflated to moderately inflated Not inflated Moderately to very inflated Not inflated Moderately to very inflated Very inflated Inflated to very inflated Moderately inflated Moderately inflated Moderately inflated Not inflated 
Orientation of teeth Diverging Diverging Diverging Diverging Diverging Parallel Parallel Diverging Parallel Diverging Diverging Diverging 
Subumbonal pit Absent Present Present Present Present Absent Absent Absent Present Absent 
3-a tooth Present Reduced or absent (often in adults) Absent Present Present Present Present Present Present Present Reduced Absent 
3-b tooth Broad Thin Thin Thin Thin Thin Thin Broad Thin Thin Thin Thin 
Posterior nymphal ridge Present Absent Absent Absent Absent Absent Absent Absent Absent Absent Absent Absent 
Pallial sinus Absent Small sinus present Absent Small sinus present Small sinus present Absent Absent Small sinus present Well developed Absent Small sinus present Absent 
Anterior pedal retractor scar Shallow Deep Shallow Shallow Deep Shallow Shallow Shallow Shallow Shallow 
Numbers of demibranchs 
Processes on inner vulva of inhalant siphon Absent Present Absent Absent 
 CalyptogenaDall, 1891 PhreagenaWoodring, 1938 EctenagenaWoodring, 1938 ArchivesicaDall, 1908 AkebiconchaKuroda, 1943 IsorropodonSturany, 1896 VesicomyaDall, 1886 PliocardiaWoodring, 1925 CallogoniaDall, 1889 WaisiuconchaBeets, 1942 HubertschenckiaTakeda, 1953 Pleurophopsisvan Winkle, 1919 
Type species Calyptogena pacificaDall, 1891 Phreagena lasiaWoodring, 1938 Calyptogena elongataDall, 1916 Vesicomya gigasDall, 1895 Akebiconcha kawamuraiKuroda, 1943 Isorropodon peplexumSturany, 1896 Callocardia atlanticaSmith, 1885 Anomalocardia bowdeniana Dall, 1903 Callocardia (Callogonia) leeanaDall, 1889 Waisiuconcha alberdinaeBeets, 1942 Tapes ezoensisYokoyama, 1890 Pleurophopsis unioidesvan Winkle, 1919 
Maximal shell size for genus (mm) 90 250 44 111 60 47 10 44 34 24 65 200 
Shell outline From elongate-elliptical to elongate Elongate Elongate From subovate to elongate-elliptical Elongate-elliptical From subcircular to subovate Subcircular Subovate Subovate Subcircular Subovate Elongate 
Tumidity Not inflated Not inflated to moderately inflated Not inflated Moderately to very inflated Not inflated Moderately to very inflated Very inflated Inflated to very inflated Moderately inflated Moderately inflated Moderately inflated Not inflated 
Orientation of teeth Diverging Diverging Diverging Diverging Diverging Parallel Parallel Diverging Parallel Diverging Diverging Diverging 
Subumbonal pit Absent Present Present Present Present Absent Absent Absent Present Absent 
3-a tooth Present Reduced or absent (often in adults) Absent Present Present Present Present Present Present Present Reduced Absent 
3-b tooth Broad Thin Thin Thin Thin Thin Thin Broad Thin Thin Thin Thin 
Posterior nymphal ridge Present Absent Absent Absent Absent Absent Absent Absent Absent Absent Absent Absent 
Pallial sinus Absent Small sinus present Absent Small sinus present Small sinus present Absent Absent Small sinus present Well developed Absent Small sinus present Absent 
Anterior pedal retractor scar Shallow Deep Shallow Shallow Deep Shallow Shallow Shallow Shallow Shallow 
Numbers of demibranchs 
Processes on inner vulva of inhalant siphon Absent Present Absent Absent 
Table 13.

List of Recent species originally described as Calyptogena or usually referred to Calyptogena, which we exclude from the genus.

Original generic assignment Species epithet Reference of original description Distinguishing features from Calyptogena 
Calyptogena (Ectenagena) australis Stuardo & Valdovinos, 1988 Narrow 3b tooth, completely reduced 3a tooth, absence of right posterior nymphal ridge, presence of pallial sinus 
Calyptogena (Calyptogena) birmani Domaneschi & Lopes, 1990 Absence of right posterior nymphal ridge, presence of pallial sinus 
Calyptogena diagonalis Barry & Kochevar, 1999 Narrow 3b tooth, absence of right posterior nymphal ridge, presence of pallial sinus, two demibranchs, inner vulva of inhalant siphon with processes 
Calyptogena (Archivesica) edisonensis Okutani, Kojima & Kim, 2004 Narrow 3b tooth, absence of right posterior nymphal ridge, presence of subumbonal pit, pallial sinus, two demibranchs, inner vulva of inhalant siphon with processes* 
Calyptogena elongata Dall, 1916 Narrow 3b tooth, absence of right posterior nymphal ridge, completely reduced 3a-tooth 
Ectenagena extenta Krylova & Moskalev, 1996 Narrow 3b tooth, absence of 3a-tooth and right posterior nymphal ridge, presence of pallial sinus, two demibranchs, horseshoe-like aperture of inhalant siphon 
Calyptogena (Ectenagena) fossajaponica Okutani, Fujikura & Kojima, 2000 Narrow 3b tooth, absence of right posterior nymphal ridge, completely reduced 3a tooth 
Calyptogena (Archivesica) garuda Okutani & Soh, 2005 Narrow 3b tooth, absence of right posterior nymphal ridge, presence of subumbonal pit, pallial sinus 
Calyptogena (Ectenagena) kaikoi Okutani & Métivier, 1986 Narrow 3b tooth, absence of right posterior nymphal ridge, completely reduced 3a tooth 
Calyptogena (Archivesica) kilmeri Bernard, 1974 Narrow 3b tooth, absence of right posterior nymphal ridge, presence of pallial sinus, two demibranchs, inner vulva of inhalant siphon with processes* 
Calyptogena (Ectenagena) laubieri Okutani & Métivier, 1986 Narrow 3b tooth, absence of right posterior nymphal ridge, presence of subumbonal pit, pallial sinus, two demibranchs, inner vulva of inhalant siphon with processes* 
Calyptogena (Ectenagena) magnifica Boss & Turner, 1980 Narrow 3b tooth, absence of right posterior nymphal ridge, presence of two demibranchs 
Calyptogena (Archivesica) magnocultellus Okutani, Kojima & Iwasaki, 2002 Narrow 3b tooth, presence of subumbonal pit and pallial sinus 
Calyptogena nankaiensis Okutani, Kojima & Ashi, 1996 Narrow 3b tooth, absence of right posterior nymphal ridge, presence of subumbonal pit, pallial sinus, two demibranchs, inner vulva of inhalant siphon with processes* 
Calyptogena (Ectenagena) nautilei Okutani & Métivier, 1986 Narrow 3b tooth, absence of right posterior nymphal ridge, presence of subumbonal pit and pallial sinus 
Calyptogena okutanii Kojima & Ohta, 1997 Narrow 3b tooth, absence of right posterior nymphal ridge, presence pallial sinus 
Calyptogena packardana Barry, Kochevar, Baxter & Harrold, 1997 Narrow 3b tooth, absence of right posterior nymphal ridge, presence of pallial sinus, two demibranchs, inner vulva of inhalant siphon with processes 
Calyptogena (Ectenagena) phaseoliformis Métivier, Okutani & Ohta, 1986 Narrow 3b tooth, completely reduced 3a tooth, absence of right right posterior nymphal ridge 
Calyptogena (Calyptogena) ponderosa Boss, 1968 Absence of right posterior nymphal ridge, presence of pallial sinus 
Calyptogena similaris Okutani, Kojima & Ashi, 1997 Narrow 3b tooth, absence of right posterior nymphal ridge, presence of pallial sinus, two demibranchs, inner vulva of inhalant siphon with processes* 
Calyptogena solidissima Okutani, Hashimoto & Fujikura, 1992 Narrow 3b tooth, absence of right posterior nymphal ridge, presence of subumbonal pit and pallial sinus 
Calyptogena soyoae Okutani, 1957 Narrow 3b tooth, absence of right posterior nymphal ridge, presence pallial sinus 
Calyptogena (Archivesica) tsubasa Okutani, Fujikura & Kojima, 2000 Narrow 3b tooth, absence of right posterior nymphal ridge, presence pallial sinus 
Original generic assignment Species epithet Reference of original description Distinguishing features from Calyptogena 
Calyptogena (Ectenagena) australis Stuardo & Valdovinos, 1988 Narrow 3b tooth, completely reduced 3a tooth, absence of right posterior nymphal ridge, presence of pallial sinus 
Calyptogena (Calyptogena) birmani Domaneschi & Lopes, 1990 Absence of right posterior nymphal ridge, presence of pallial sinus 
Calyptogena diagonalis Barry & Kochevar, 1999 Narrow 3b tooth, absence of right posterior nymphal ridge, presence of pallial sinus, two demibranchs, inner vulva of inhalant siphon with processes 
Calyptogena (Archivesica) edisonensis Okutani, Kojima & Kim, 2004 Narrow 3b tooth, absence of right posterior nymphal ridge, presence of subumbonal pit, pallial sinus, two demibranchs, inner vulva of inhalant siphon with processes* 
Calyptogena elongata Dall, 1916 Narrow 3b tooth, absence of right posterior nymphal ridge, completely reduced 3a-tooth 
Ectenagena extenta Krylova & Moskalev, 1996 Narrow 3b tooth, absence of 3a-tooth and right posterior nymphal ridge, presence of pallial sinus, two demibranchs, horseshoe-like aperture of inhalant siphon 
Calyptogena (Ectenagena) fossajaponica Okutani, Fujikura & Kojima, 2000 Narrow 3b tooth, absence of right posterior nymphal ridge, completely reduced 3a tooth 
Calyptogena (Archivesica) garuda Okutani & Soh, 2005 Narrow 3b tooth, absence of right posterior nymphal ridge, presence of subumbonal pit, pallial sinus 
Calyptogena (Ectenagena) kaikoi Okutani & Métivier, 1986 Narrow 3b tooth, absence of right posterior nymphal ridge, completely reduced 3a tooth 
Calyptogena (Archivesica) kilmeri Bernard, 1974 Narrow 3b tooth, absence of right posterior nymphal ridge, presence of pallial sinus, two demibranchs, inner vulva of inhalant siphon with processes* 
Calyptogena (Ectenagena) laubieri Okutani & Métivier, 1986 Narrow 3b tooth, absence of right posterior nymphal ridge, presence of subumbonal pit, pallial sinus, two demibranchs, inner vulva of inhalant siphon with processes* 
Calyptogena (Ectenagena) magnifica Boss & Turner, 1980 Narrow 3b tooth, absence of right posterior nymphal ridge, presence of two demibranchs 
Calyptogena (Archivesica) magnocultellus Okutani, Kojima & Iwasaki, 2002 Narrow 3b tooth, presence of subumbonal pit and pallial sinus 
Calyptogena nankaiensis Okutani, Kojima & Ashi, 1996 Narrow 3b tooth, absence of right posterior nymphal ridge, presence of subumbonal pit, pallial sinus, two demibranchs, inner vulva of inhalant siphon with processes* 
Calyptogena (Ectenagena) nautilei Okutani & Métivier, 1986 Narrow 3b tooth, absence of right posterior nymphal ridge, presence of subumbonal pit and pallial sinus 
Calyptogena okutanii Kojima & Ohta, 1997 Narrow 3b tooth, absence of right posterior nymphal ridge, presence pallial sinus 
Calyptogena packardana Barry, Kochevar, Baxter & Harrold, 1997 Narrow 3b tooth, absence of right posterior nymphal ridge, presence of pallial sinus, two demibranchs, inner vulva of inhalant siphon with processes 
Calyptogena (Ectenagena) phaseoliformis Métivier, Okutani & Ohta, 1986 Narrow 3b tooth, completely reduced 3a tooth, absence of right right posterior nymphal ridge 
Calyptogena (Calyptogena) ponderosa Boss, 1968 Absence of right posterior nymphal ridge, presence of pallial sinus 
Calyptogena similaris Okutani, Kojima & Ashi, 1997 Narrow 3b tooth, absence of right posterior nymphal ridge, presence of pallial sinus, two demibranchs, inner vulva of inhalant siphon with processes* 
Calyptogena solidissima Okutani, Hashimoto & Fujikura, 1992 Narrow 3b tooth, absence of right posterior nymphal ridge, presence of subumbonal pit and pallial sinus 
Calyptogena soyoae Okutani, 1957 Narrow 3b tooth, absence of right posterior nymphal ridge, presence pallial sinus 
Calyptogena (Archivesica) tsubasa Okutani, Fujikura & Kojima, 2000 Narrow 3b tooth, absence of right posterior nymphal ridge, presence pallial sinus 

*Data of authors.

Our concept of Calyptogena is supported by molecular investigations. Preliminary molecular studies on C. pacifica, C. rectimargo, C. makranensis and C. costaricana indicate that they form a well-supported monophyletic group separated from other known vesicomyid groups (Goffredi, personal communication). This cluster also includes those species closely related to C. pacifica, which have been termed the ‘pacifica-lepta’ complex (Peek et al., 1997; Goffredi et al., 2003). Goffredi et al. (2003) showed evidence for five putative species at 15 localities in the eastern Pacific Ocean, including C. pacifica and Vesicomya lepta (Dall, 1896), with three probable new species. Some of these putative new species may be identical to the species described in this study. However, further investigations are needed to resolve this. In addition, the recent publication by Kojima et al. (2004) indicated the placement of C. fausta in the ‘pacifica-lepta’ complex.

The close proximity of V. lepta to C. pacifica in the molecular tree is puzzling; therefore, we studied the type material of V. lepta, with the aim of ascertaining its relationship to Calyptogena. We found that V. lepta differs from ‘typical’ Calyptogena in having a much more convex ventral shell margin, a well-developed lunule and lacks a right posterior nymphal ridge. At the same time, V. lepta shares features with Calyptogena such as the presence of an escutcheon, a broad posterior ramus (3b) of the right subumbonal cardinal tooth and the absence of the pallial sinus. In conclusion, we hesitate to assign V. lepta to the genus Calyptogena. Additional studies of anatomy and the variability of shell characters of V. lepta are needed. Furthermore, it needs to be confirmed that the species investigated genetically is actually identical to the type material of V. lepta.

The taxa most closely related to Calyptogena are probably the genus IsorropodonSturany, 1896, and the group of species, including ‘Calyptogena’ phaseoliformisMétivier, Okutani & Ohta, 1986, ‘C’. kaikoiOkutani & Métivier, 1986 and ‘Calyptogena’ n. sp. from Logatchev (Peek et al., 2000). These three groups have several characters in common, such as the absence of a pallial sinus, the presence of a single inner pair of demibranchs and the absence of dendritic processes on the inner vulva of the inhalant siphon. The close relationship of Calyptogena with the ‘phaseoliformis’ – group is also supported by Horikoshi (1989), who pointed out the similarity of hinge structure in C. pacifica, ‘C’. phaseoliformis and ‘C’. kaikoi. Molecular data have also revealed the affinity of C. fausta with ‘C’. phaseoliformis and ‘C’. kaikoi (Kojima et al., 1995). Nevertheless, there are considerable differences in the shell shape and hinge margins, which separate Calyptogena from both Isorropodon and the ‘phaseoliformis’ – group. Calyptogena is distinguished from Isorropodon by a larger, thicker shell, a broader hinge line with radiating teeth and the presence of a posterior nymphal ridge in the right valve (Table 12). From the ‘phaseoliformis’ – group, Calyptogena differs by its shorter, more elliptical shell with a well-marked escutcheon and a much stronger hinge plate. Species of the “phaseoliformis” – group lack the anterior ramus of the subumbonal cardinal and the posterior nymphal ridge in the right valve. Also, in the ‘phaseoliformis’ – group the interlamellar septa of the demibranchs are divided into separate cylindrical tubes (Fiala-Médoni & Le Pennec, 1988; Southward et al., 2001; unpublished observations), whereas in Calyptogena the interlamellar septa are not divided. Quite probably the ‘phaseoliformis’ – group should be placed in the genus Pleurophopsisvan Winkle (1919), based on the fossil middle Tertiary species P. unioides from Trinidad (van Winkle, 1919).

The bacteria-containing gill of Calyptogena with its entirely reduced outer demibranchs and wide interlamellar septa is one of the most specialized in the family Vesicomyidae. The specialized gill may reflect ecological adaptations that have been studied in two species belonging to different vesicomyid genera, C. pacifica and ‘C.’ kilmeri. The different physiologies were shown to be related to different pore water compositions leading to spatial segregation of these two species within a seep site (Barry, Kochevar & Baxter, 1997). The physiological adaptations include differences in, for example, the sulphide-binding affinity of the blood, the sulphide consumption rates and densities of bacterial symbionts, as well as different growth rates (Barry & Kochevar, 1998; Goffredi & Barry, 2002). It might be expected that these physiological peculiarities are typical not merely for C. pacifica, but for the entire genus Calyptogena. This may allow niche differentiation amongst coexisting vesicomyid genera. Further examples are in the Sea of Okhotsk with the occurrence of C. rectimargo together with Akebiconcha soyoae ochotensisScarlato, 1981 and Archivesica ochoticaScarlato, 1981 (Sahling et al. 2003, unpubl.), as well as the Yukie Ridge in the Nankai Trough with coexisting C. fausta and ‘C.’ similaris (Kojima & Ohta, 1997).

Calyptogena's endosymbionts, and thus Calyptogena species themselves, rely on energy-rich hydrogen sulphide for chemotrophy. At methane seeps (cold seeps) this is produced by the anaerobic oxidation of methane. At hydrothermal vents it is provided by the hydrothermal fluids that are enriched in reduced compounds due to seawater circulation through the upper ocean crust. Despite the vast geological differences there is evidence that sediment-covered hydrothermal vents and methane seeps can be geochemically similar and that the concentration and flux of sulphide is a key factor in understanding the distribution of chemosynthetic species (Sahling et al., 2005). We lack data on the geochemical habitat for all Calyptogena species, with the exception of C. pacifica off Monterey and Oregon (Barry, Kochevar & Baxter, 1997; Sahling et al., 2002). In general, most species occur in areas with methane seepage: C. goffrediae off Peru (Olu et al., 1996), C. costaricana of Costa Rica (Mau et al., 2006), C. rectimargo in the Sea of Okhotsk (Greinert et al., 2002; Sahling et al., 2003), C. makranensis off Pakistan (von Rad et al., 2000), C. fausta off Japan (Henry et al., 2002) and C. valdivia in the Gulf of Guinea (Sibuet et al., 2002). The geochemical habitat of C. pacifica at Piip Volcano in the Bering Sea is very similar to that of methane seeps, too. Warm fluids circulate through sediments causing the dissolution of gas hydrate and, subsequently, the release of methane (Taran et al., 1992). Calyptogena starobogatovi is the only species that occurs at a hydrothermal vent, southwest of the caldera of Axial Seamount on the Juan de Fuca Ridge. We agree with Goffredi et al. (2003), who also found species at Juan de Fuca Ridge which they discuss as not specific to the hydrothermal vent system, but restricted to the bathymetric depths at which the hydrothermal vent is located. The authors found that the putative ‘Vesicomya sp. mt-II’ (which is probably identical to C. starobogatovi) is not only present at hydrothermal vents, but also at methane seeps occurring at a narrow bathymetric range between 1500 and 2200 m. Similar results were found off Japan, where vesicomyid clams were found at hydrothermal vents as well as methane seeps within restricted vertical ranges (Kojima & Ohta, 1997; Fujikura et al., 2000). In this study, we also found a remarkably narrow bathymetric range for C. pacifica, between about 500 and 950 m within a wide geographic range from the Bering Sea to Monterey Bay off California. The depth as well as the geographic range for all other Calyptogena species is not well defined due to the limited sampling. Only C. valdiviae has a wide distribution along the continental margin of Africa. In addition, dead shells were found at a wide variety of depths between 500 and 2500 m. Most Calyptogena species occur along continental margins (Fig. 23), suggesting that these are major spreading pathways. Methane seepage is a widespread phenomenon that is not limited to tectonically active compressional margins, e.g. off Pakistan (von Rad et al., 2000) or the Circum-Pacific ‘fire belt’ in which the seeps off Japan (Henry et al., 2002), Oregon (Sahling et al., 2002), California (Barry et al., 1996), Costa Rica (Mau et al., 2006) and Peru (Olu et al., 1996) are located. It is also caused by various geological processes such as salt tectonics, faults tapping into methane-rich sediments or landslides. Respective examples are the pockmarks in the Gulf of Guinea (Sibuet et al., 2002), the gas seeps in the Sea of Okhotsk (Sahling et al., 2003) and the slump off Peru (Olu et al., 1996). Intensive research in areas such as the continental margin off Japan (Kojima, 2002) and California (Barry et al., 1996) revealed very high frequencies of individual methane seeps. Despite the small spatial scale of individual methane seeps, we suggest that the various geological phenomena leading to abundant seep sites result in a near-continuous linear system along continental margins through which vesicomyid clams can spread. We further propose that geographic isolation is a major factor for the speciation within the genus Calyptogena. Molecular studies support the view that vesicomyid clams spread easily along continental margins. Kojima et al. (2004) recognized six pairs of closely related vesicomyid species, each comprising one species from the western Pacific and one from the eastern Pacific, which indicates multiple migrations across the Pacific. Furthermore, molecular phylogenies indicate that vesicomyid clams have diversified at methane seeps and, later, have also exploited hydrothermal vents and decomposing whale bones (Peek et al., 1997, 2000; Baco et al., 1999).

Figure 23.

Distribution of Calyptogena species based on the material examined in this study.

Figure 23.

Distribution of Calyptogena species based on the material examined in this study.

Among numerous fossils of vesicomyids, only some can be more or less certainly referred to Calyptogena. All these species (Table 14) are characterized by the presence of an escutcheon, the absence of a pallial sinus and a dentition which fits the diagnosis of Calyptogena. The species C. moraiensis (Suzuki, 1941) may be synonymous with C. pacifica (Boss & Turner, 1980; Okutani, 1962). Calyptogena gibberaCrickmay (1929) was also considered a possible synonym of C. pacifica (Boss & Turner, 1980), but a recent complete redescription of C. gibbera shows that it differs markedly from C. pacifica (Squires, 1991). The distinguishing features are the presence of a short hinge plate with narrow 3b-tooth in right valve, short 4b-tooth in the left valve and the absence of the right posterior nymphal ridge, which indicate that C. gibbera is not a representative of the genus Calyptogena s.s. Calyptogena (Calyptogena) chinookensiisSquires & Goedert, 1991, known from late middle Eocene to late Oligocene of Washington, is also characterized by a short hinge plate with diverging teeth without nymphal ridge in the right valve. Thus, we suggest that it should be excluded from the genus Calyptogena s.s.

Table 14.

Palaeontological records of Calyptogena.

Species Age Region Reference 
C. pacifica Pliocene California Grant & Gale, 1931 
C. pacifica Miocene, Pliocene Honshu, Japan Kanno et al., 1989 
C. moraiensis Mio-Pliocene Japan Suzuki, 1941 
C. panamensis Uppermost Miocene and lower Pliocene Costa-Rica and Panama, Pacific Coast Olsson, 1942 
Species Age Region Reference 
C. pacifica Pliocene California Grant & Gale, 1931 
C. pacifica Miocene, Pliocene Honshu, Japan Kanno et al., 1989 
C. moraiensis Mio-Pliocene Japan Suzuki, 1941 
C. panamensis Uppermost Miocene and lower Pliocene Costa-Rica and Panama, Pacific Coast Olsson, 1942 

The earliest records for the entire family Vesicomyidae are from the early Cretaceous (Kanie & Sakai, 1997). The first representatives of Calyptogena appeared later, with a first record in the Miocene (Table 14) in the northwestern and north Pacific. Later records of Calyptogena s.s. date from the uppermost Miocene of the eastern Pacific. The earliest fossil records in combination with the observed high diversity of Recent species in the northwest Pacific (Fig. 23) suggets that this was the site of origination of the genus. The modern distribution of Calyptogena s.s. leads to the hypothesis that dispersal of the genus took place from the northwestern Pacific in two main directions: to the East Pacific along the continental margin of North America and to the west into the Indian Ocean via abundant seep sites in the Indo-West Pacific region. Colonization of the Atlantic Ocean could have been accomplished along the continental margin of Africa, reflected in the distribution pattern of C. valdiviae.

ACKNOWLEDGEMENTS

We are obliged to the captains and crews as well as the pilots and technicians of the submersibles Mir and Alvin for their support in collecting the samples during the 12 cruises. The authors are grateful to P. Linke, E. Suess, L.I. Moskalev, S.V. Galkin and A.V. Gebruk for providing clam specimens. We thank J. Barry and R. Kochevar for making available the material of C. pacifica from Monterey Bay, and B. Vrijenhoek and S. Goffredi for providing us with voucher specimens from the East Pacific. For loan of type material we thank T. Nickens and J. Harasewych (NMNH), B. Sirenko (ZIN RAN), Y. Fujiwara and H. Saito (NSMT) as well as M. Glaubrecht (ZMB). We are indebted to Ya.I. Starobogatov and L.I. Moskalev (IO RAN) for the stimulating discussion and to A.N. Mironov (IO RAN) for a critical review of an earlier version of this paper. We greatly thank E. Coan and two anonymous reviewers as well as the associate editor J. Taylor for their very constructive criticism. This study was partly funded by the DFG-Research Centre Ocean Margins of the University of Bremen no. RCOM0382. In addition, funding for E.K. was provided by the Russian Foundation for Basic Research (project number 05-05-65283), and the ‘Deutsche Forschungsgemeinschaft’ (project number 436RUS17/50/05).

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Miocene Mollusca from Bowden Jamaica. Pelecypods and scaphopods
Carnegie Institution of Washington Publication
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1925
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WOODRING
W.P.
Lower Pliocene mollusks and echinoids from the Los Angeles Basin, California
United States Geological Survey Professional Paper
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1938
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YOKOYAMA
M.
Versteinerungen aus der japanischen Kreide
Palaeontographica
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1890
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