Abstract

Trawl surveys off Western Australia and seamounts south of New Caledonia at depths between 375 and 545 m have yielded two species of a previously unknown genus of benthic octopus (Family: Octopodidae). Histoctopus n. gen. is described here and contains two new species, Histoctopus discus and Histoctopus zipkasae n. spp. The most distinctive morphological feature of this new genus is extreme web margin development along the length of the arms, widening towards the distal tips. Of all benthic octopuses, such web margin development only occurs in this new genus and three other distinct genera, Graneledone, Pteroctopus and Velodona (from comparable depths, typically >200 m). Due to significant morphological differences between these two genera and Histoctopus, we propose that the shared web margin development reflects convergence that is peculiar to a deeper-water habitat. The function of these web extensions remains unknown; they may aid in ensnaring or enveloping prey and/or provide lift while jet swimming off the seafloor.

INTRODUCTION

Over the past 30 years, slope and deep-water trawl surveys in the Australasian region by French and Australian researchers have been uncovering diverse and largely unknown assemblages of benthic organisms (Bouchet & Metivier, 1982; Richer de Forges, 1990; Richer de Forges, Koslow & Poore, 2000; Valdéz, 2001a, b; Valdéz & Gosliner, 2001). Amongst the material collected have been many new and distinctive benthic octopus taxa (Norman, Hochberg & Lu, 1997; Norman, Boucher & Hochberg, 2004; Norman, Hochberg & Boucher-Rodoni, 2004, 2005).

In Australia, trawl surveys by the Australian Commonwealth Scientific and Research Organization (CSIRO) between 1982 and 1989 at depths of 375–458 m on the Northwest Shelf off northern Western Australia collected a distinctive new mesobenthic octopus with extreme web margin development. Around the same time, repeated visits (1986, 1989, 2001) by French researchers to a seamount system, the Sponge Bank off New Caledonia, yielded a second species with similar web development from depths of 500 to 545 m. The mature males of this second species possess dramatically enlarged suckers.

In 2005, deployment of still and video camera equipment at depth off the Western Australian coast by the CSIRO captured images of live individuals of the new Australian species foraging over soft sediment and low-relief rocky areas at depths of 384 to 449 m.

On detailed examination, dissection and description, it was clear that these two species represented members of a new mesobenthic genus, described here as Histoctopus n. gen. The presence of an ink sac clearly distinguished this taxon from other deeper water genera that lack an ink sac, namely Benthoctopus Grimpe, 1921 and Bathypolypus Grimpe, 1921. The presence of two rows of suckers per arm clearly distinguished it from deep-water genera that possess a single row of suckers, such as Graneledone Joubin, 1918, Microeledone Norman, Hochberg & Boucher-Rodoni, 2004, Thaumeledone Robson, 1930, Bentheledone Robson, 1932 and Velodona Chun, 1915. The closest morphological similarities are with the mesobenthic genera Scaeurgus Troschel, 1857 and GaleoctopusNorman, Boucher & Hochberg, 2004.

Recent molecular studies indicate that the genus Octopus as it has historically been treated is paraphyletic (Guzik, Norman & Crozier, 2005; Strugnell et al., 2005). It represents a catchall genus encompassing diverse and unrelated groups. As a consequence, the genus has recently been restricted to Octopus sensu stricto, containing the type species, Octopus vulgaris Cuvier, 1797, and members of the ‘Octopus vulgaris species group’ (see Norman & Hochberg, 2005). Distinct subgenera and species groups within the family Octopodidae that had previously been placed in the genus Octopus are now being revaluated, with a number being raised to generic rank (i.e. Huffard & Hochberg, 2005 for Amphioctopus; Norman & Hochberg, 2005a for Abdopus; Norman & Hochberg, 2005b for Thaumoctopus; Hochberg, Norman & Finn, 2006 for Wunderpus).

MATERIAL AND METHODS

Indian Ocean specimens examined in this study originated from CSIRO benthic trawl surveys by the FRV Soela in 1982 and 1984 and from observers on board commercial fishing vessels (FV Courageous, Striker and Surefire) in 1988 and 1989. Still images of live octopuses were obtained by CSIRO on board the FRV Southern Surveyor in 2005, using headrope still and video cameras.

Pacific Ocean material examined in this study resulted from research campaigns off New Caledonia and the Coral Sea: CHALCAL 2, 1986; SMIB 4, 1989; NORFOLK 1, 2001. Three gear types were used in capture of this species: Waren dredge, (‘Drague Waren’, station code: DW), Fish trawl (‘chalut à perche’, station code: CP) and shrimp trawl (‘chalut à panneaux [crevettes]’, station code: CC).

Type material for the new species described here is lodged in the cephalopod collections of Museum Victoria (MV), Melbourne, Australia and the Muséum national d'Histoire naturelle (MNHN), Paris.

Morphological characters and measurements used in the descriptions below follow Roper & Voss (1983) and Norman & Sweeney (1997). Where sufficient specimens exist, ranges are presented as ‘minimum–mean–maximum’. Diagnoses and descriptions presented here are based on submature and mature specimens. Data for juvenile material are not included here as counts and relative measurements [such as sucker counts and arm lengths vs mantle length (ML)] undergo considerable ontogenetic change in the early growth stages of octopuses and can cause overlap in otherwise valid diagnostic characters.

SYSTEMATIC DESCRIPTIONS

Family Octopodidae d'Orbigny, 1840
Histoctopus new genus

Type species: Histoctopus zipkasae n. gen., n. sp.

Etymology: From the Greek ‘histos’ for web or tissue, referring to the wide and flared web margins characteristic of members of this new genus.

Diagnosis: Small to medium-size mesobenthic species. Mantle muscular, globose to rounded ovoid. Stylets present, long, chitinous (mineralized). Arms: muscular, medium length, 2.5–3.8 times ML; approximately equal in length, lateral arms slightly shorter (typically 2 > 3 > 4 > 1 or 3 > 2 > 4 > 1). Arm autotomy at distinct plane absent. Web: moderate to deep, deepest around 20–30% of longest arm; approximately equal in depth, slightly deeper on lateral arms (typically B = C = D = E = A). Web margins on ventral arms very wide, form loose semi-transparent membranes in preserved material. Interbrachial web pouches absent. Suckers in two rows. Enlarged suckers present on all arms in mature males. Funnel organ W-shaped. Gills with eight to nine lamellae per demibranch. Radula with nine elements, seven rows of teeth plus marginal plates. Rhachidian tooth with two to three lateral cusps in asymmetrical seriation. Posterior salivary glands moderate to large, approximately equal in length with buccal mass. Distinct crop present as side-branch off oesophagus. Ink sac and anal flaps present. Third right arm of male hectocotylized, 75–85% length of opposite arm. Ligula of moderate size, 4.5–8% of hectocotylized arm length, triangular to spoon-shaped with open groove and lacking raised transverse laminae. Calamus large and pronounced, c. 40–60% of ligula length. Terminal organ (penis) large and T-shaped with diverticulum longer than distal portion. Spermatophores large (equal to or longer than ML), bulbous with swollen short sperm reservoir containing few coils (<10) of sperm cord coiled in a double strand. Distal tip of spermatophore storage sac with reticulate glandular tissue. Eggs (where known) of moderate size (6.5–8 mm, 7–9% of ML). Colour patterns orange brown dorsally, cream ventrally. Transverse rows of small white papillae/leucophores visible on dorsal mantle in live animal and in some preserved material. False eye-spots (ocelli) absent. Skin sculptured with evenly spaced small rounded papillae. Skin ridge around lateral margin of mantle absent.

Taxonomic remarks: Histoctopus n. gen. is discriminated from other octopodid genera that possess an ink sac in Table 1. The genus Octopus s.s. Cuvier, 1797 is clearly distinguished by the absence of extreme web margin development (vs present in Histoctopus), a small ligula (c. <3 vs 4.5–8%), a simple linear terminal organ with small diverticulum (vs a T-shaped terminal organ with large diverticulum), absence of a distinct swollen glandular organ on the proximal spermatophore storage sac (vs present), and small, almost linear spermatophores with a singly coiled sperm cord (vs large bulbous spermatophores with a double-plaited sperm cord in Histoctopus).

Table 1.

Comparison of slope and deep-water genera that possess an ink sac with Octopus s.s. (Octopodidae).

 Octopus s.s. Cuvier, 1797 Histoctopus n. gen. Scaeurgus Troschel, 1857 Pteroctopus Fisher, 1882 GaleoctopusNorman et al., 2004 Velodona Chun, 1915 
Source Unpubl. data This study Norman et al. (2005) Norman et al. (1997) and unpubl. data Norman et al. (2004) Unpubl. data 
Number of species 10 + 6 + 
Max mantle length (ML) in mm 250 107 90 130 37 150 
Number of sucker rows 
Hectocotylized arm side Right Right Left Left or right Right Right 
Arm length (×ML) 3–6 2.4–3.7 2–3.3 2.8–3.8 2.7–4.4 3–4.5 
Arm formula 3 = 2 > 4 > 1 4 = 3 = 2 > 1 3 = 2 > 4 > 1 Subequal 4 = 3 = 2 > 1 1 > 2 > 3 > 4 
Gill lamellae count 6–11 8–9 8–13 8–10 10–11 9–11 
Flared distal webs Absent Present Absent Present Absent Present 
Stylet mineralization* Absent Present Present Absent Absent Absent 
Pallial aperture Wide (c. 50%) Wide (c. 50%) Wide (c. 50%) Narrow (<40%) Wide (c. 50%) Wide (c. 50%) 
 (% circumference) 
Funnel Organ shape V V V V 
Enlarged suckers on arms of males Arms 2–3 + All arms Arms 2–3 + Absent Absent Absent 
Ligula shape Triangular to spoon-shaped with open groove Spoon- to leaf-shaped with open groove Double-peanut shaped, deep groove Broad, conical with open groove Barrel-shaped with transverse lug-lined pit as ligula groove Elongate triangular with open groove and thick margins 
Ligula length(% HAL) typically <3%** 4.5–8 5–14 5–11 11–20 6–9 
Calamus length (% of ligula length) 15–60 40–60 20–70 30–45 55–75 30–34 
Terminal shape Linear T-shaped Linear Linear 6-shaped 6-shaped 
Terminal organ diverticulum size Small Large Small Small Moderate Moderate 
Spermatophore length (×ML) 0.3–0.8 0.9–1.6 1.2–1.6 0.5–0.9 0.7–1.2 0.8–1.1 
Sperm cord Single Plaited double Plaited double Single Single Single 
Lateral ridge Absent Absent Present Absent Present Absent 
 Octopus s.s. Cuvier, 1797 Histoctopus n. gen. Scaeurgus Troschel, 1857 Pteroctopus Fisher, 1882 GaleoctopusNorman et al., 2004 Velodona Chun, 1915 
Source Unpubl. data This study Norman et al. (2005) Norman et al. (1997) and unpubl. data Norman et al. (2004) Unpubl. data 
Number of species 10 + 6 + 
Max mantle length (ML) in mm 250 107 90 130 37 150 
Number of sucker rows 
Hectocotylized arm side Right Right Left Left or right Right Right 
Arm length (×ML) 3–6 2.4–3.7 2–3.3 2.8–3.8 2.7–4.4 3–4.5 
Arm formula 3 = 2 > 4 > 1 4 = 3 = 2 > 1 3 = 2 > 4 > 1 Subequal 4 = 3 = 2 > 1 1 > 2 > 3 > 4 
Gill lamellae count 6–11 8–9 8–13 8–10 10–11 9–11 
Flared distal webs Absent Present Absent Present Absent Present 
Stylet mineralization* Absent Present Present Absent Absent Absent 
Pallial aperture Wide (c. 50%) Wide (c. 50%) Wide (c. 50%) Narrow (<40%) Wide (c. 50%) Wide (c. 50%) 
 (% circumference) 
Funnel Organ shape V V V V 
Enlarged suckers on arms of males Arms 2–3 + All arms Arms 2–3 + Absent Absent Absent 
Ligula shape Triangular to spoon-shaped with open groove Spoon- to leaf-shaped with open groove Double-peanut shaped, deep groove Broad, conical with open groove Barrel-shaped with transverse lug-lined pit as ligula groove Elongate triangular with open groove and thick margins 
Ligula length(% HAL) typically <3%** 4.5–8 5–14 5–11 11–20 6–9 
Calamus length (% of ligula length) 15–60 40–60 20–70 30–45 55–75 30–34 
Terminal shape Linear T-shaped Linear Linear 6-shaped 6-shaped 
Terminal organ diverticulum size Small Large Small Small Moderate Moderate 
Spermatophore length (×ML) 0.3–0.8 0.9–1.6 1.2–1.6 0.5–0.9 0.7–1.2 0.8–1.1 
Sperm cord Single Plaited double Plaited double Single Single Single 
Lateral ridge Absent Absent Present Absent Present Absent 

HAL, hectocotylized arm length. *Mineralization often dissolves in unbuffered preservation, presence indicates detection in at least some specimens. **4.5 % in a single member species, O. tehuelchus.

The glandular organ on the spermatophore storage sac is reported for the first time. It is possible that this tissue produces some form of lubricant to aid the transmission of the large bulbous spermatophores.

Flared distal web margins occur in three other deeper-water octopodid genera, Velodona Chun, 1915, Graneledone Joubin, 1918 and Pteroctopus Fisher, 1882. The genera Velodona and Graneledone are easily distinguished from Histoctopus by the possession of only a single row of suckers. The genus Pteroctopus is also easily distinguished by its semi-gelatinous skin (vs muscular in Histoctopus), very narrow mantle opening (<40% of mantle circumference vs c. 50%), narrow-limbed VV funnel organ (vs a broad-limbed W) and paired elongate supraocular papillae over each eye (vs absent). At least one Pteroctopus species also has left-handed hectocotylization (vs right in Histoctopus).

The genus Histoctopus shares certain morphological characters with the mesobenthic octopus genera Scaeurgus Troschel, 1857 and GaleoctopusNorman, Boucher & Hochberg, 2004.

Histoctopus and Scaeurgus possess large (and typically mineralized) stylets and a double-plaited sperm cord. Males of Scaeurgus are easily distinguished by left-handed hectocotylization (vs right-handed in Histoctopus), a bulbous peanut-shaped ligula with deep ligula groove (compared with an open triangular to spoon-shaped ligula), and possession of a lateral mantle ridge (vs absent in Histoctopus).

Histoctopus and Galeoctopus share similar arm lengths, arm formulae and spermatophore lengths (relative to ML); however, they differ in that Galeoctopus lacks flared web margins, enlarged suckers, and a glandular organ on the tip of the spermatophore storage sac. It also possesses a significantly shorter hectocotylized arm (c. 40–60% of opposite arm length vs c. 80% in Histoctopus), a lateral mantle skin ridge and a unique large, barrel-shape ligula (11–20% of arm length) with a deep transverse ligula groove, the floor of which contains paired raised papillae. The spermatophores of Galeoctopus are narrow with singly coiled sperm cord in 50–90 coils (vs bulbous with <10 doubly coiled sperm cord whorls).

In general, body form, skin patterns and sculpture, the genus Histoctopus is similar to Scaeurgus and Galeoctopus. The origins of (and phylogenetic relationships among) these taxa remain unknown and await thorough molecular and biogeographic analyses.

Histoctopus discus new species
(Figs 1–4)

Type Material: Holotype: New Caledonia South: M: 51.5 mm ML, MNHN 3803, Norfolk Ridge, Sponge Bank, N/O ‘Alis’, Campagne NORFOLK 1, stn CP1687, 24°54′S, 168°22′E, 539–545 m, coll. Lozouet, Boisselier and Richer-IRD, 23 June 2001. Paratypes: New Caledonia South: 1M: 44.4 mm ML, MNHN 2108, Sponge Bank, N/O ‘Coriolis’, CHALCAL 2, stn. CC1, 24°55′S, 168°22′E, 500 m, coll. Bouchet, Metivier and Richer de Forges, 28 Oct 1986. 2M: 46.7, 41.2 mm ML, MNHN 2109, Sponge Bank, N/O ‘Alis’, Campagne SMIB 4, stn. DW34, 24°55′S, 168°22′E, 510–515 m, coll. ORSTOM, 7 March 1989.

Etymology: Latin for disk or circular plate, referring to the enlarged plate-like suckers found in mature males of this species.

Diagnosis: Small to moderate-sized species, ML to at least 51 mm. Arm lengths approximately three times ML (longest 2.8–3.5 × ML). Arms approximately equal in length, dorsal arms slightly shorter. Web sectors very thin and membranous, deep, up to 30% of longest arm length. Webs approximately equal in depth, lateral webs slightly deeper. Webs extend as membranous flared margins along entire length of all arms (including hectocotylized arm), very well developed in distal 25% of arm length with arm tips free. Suckers forming two rows. Suckers to around 145 on normal arms. Hectocotylized arm with 72–79 suckers. Three to five extremely enlarged and flattened suckers present on all arms of mature males, diameter up to 21% of ML at level of 6th to 10th proximal sucker. Large W-shaped funnel organ. Eight and nine gill lamellae per demibranch. Ink sac and anal flaps present. Third right arm hectocotylized. Ligula small to moderate (5.6 and 8.0% of arm length in two intact mature males), spoon to leaf-shaped with wide, open groove, floor with around 10–12 simple transverse creases. Calamus large and prominent, around 50% of ligula length (44.4–59.7%). Spermatophores large (1.2–1.6 × ML), few (1–4 in three mature males). Females unknown. Colour pattern: Orange brown dorsally, cream ventrally, four darker brown patches as two pairs on anterior dorsal mantle separated by strip of cream-coloured papillae. Skin sculpture: Small, round papillae uniformly scattered on all dorsal surfaces; slightly larger papilla present on posterior tip of mantle. Larger supraocular papillae absent. Lateral mantle ridge absent.

Description: Counts and measurements are presented in Table 2. The following description is based on four males (three mature and one late submature).

Medium-size muscular species (Figs 1A, 4A); ML to at least 51.1 mm, total length to at least 238 mm; weight to at least 96 g. Mantle ovoid to pear-shaped, longer than wide (width 76.0–83.0–91.2% of ML). Head wide (60.4–63.8–70.7% of ML; 72.6–76.9–79.4% of mantle width). Skin firm, sculptured and pigmented. Eyes large. Stylets: large, robust, mineralized rods (Fig. 1B), length around 40% of ML (20 mm in 51.1 and 44.4 mm ML males, MNHN 3803 and 2108). Mantle opening wide, c. 50% of circumference of body at level of opening. Funnel: moderate length, c. 40% of ML (38.2–39.5–46.2% of ML), free portion moderate to long, c. 40–50% of funnel length (31.1–38.6–44.7%). Funnel organ: W-shaped (Fig. 1C), lateral limbs slightly shorter than (or equal to) median ones (lateral limbs 73.7–84.7–100.0% of median limbs); occupies c. 60% (49.7–57.3–63.4%) of funnel length.

Figure 1.

Histoctopus discus n. gen., n. sp. A. Dorsal whole animal, 41.2 mm ML male paratype (MNHN 2109). B. Stylet, 44.4 mm ML paratype (MNHN 2108). C. Funnel organ, 46.7 mm ML paratype (MNHN 2109). D. Ligula, 46.7 mm ML paratype (MNHN 2109). Scale bars: A = 20 mm; B = 10 mm; C = 5 mm; D = 5 mm.

Figure 1.

Histoctopus discus n. gen., n. sp. A. Dorsal whole animal, 41.2 mm ML male paratype (MNHN 2109). B. Stylet, 44.4 mm ML paratype (MNHN 2108). C. Funnel organ, 46.7 mm ML paratype (MNHN 2109). D. Ligula, 46.7 mm ML paratype (MNHN 2109). Scale bars: A = 20 mm; B = 10 mm; C = 5 mm; D = 5 mm.

Table 2.

Histoctopus discus n. gen., n. sp.: counts and measurements (mm).

Repository MNHN MNHN MNHN MNHN 
Catalogue number 3803 2108 2109 2109 
Status Holotype Paratype Paratype Paratype 
Sex Male Male Male Male 
Maturity Mature Mature Mature Submature 
Total length 238 210 171 + 170 
Total wet weight (g) 95.7 75.1 49.1 39.4 
Dorsal mantle length 51.1 44.4 46.7 41.2 
Ventral mantle length 39.0 37.7 33.7 26.1 
Mantle width 41.7 40.5 35.5 34.3 
Head width 32.6 31.4 28.2 24.9 
Funnel length 19.5 20.5 16.4 15.8 
Free funnel length 8.7 7.0 5.1 7.7 
Funnel organ length 
 Lateral limb 9.7 10.4 7.3 7.5 
 Medial limb 9.7 13.0 9.9 8.8 
Web depths (L, R) 
 A 25 19 25 18 
 B 32, 32 30, 25 30, d 24, 27 
 C d, 37 36, 35 29, d 29, 34 
 D 38, 35SpG 36, 34SpG d, d 35, 33SpG 
 E 31 31 25 
Web depth formula C = D > B = E > A C = D > B = E > A  C = D > B = E > A 
Arm lengths (L, R) 
 1 152, 160 143, d 118, d 90, 102 
 2 175, 163 154, 154 116d?, d 114, 114 
 3 d (L) d (L) 112 (L) 117 (L) 
 Hc (R) 127 113 99 
 4 161, 157 147, d d, d 106, 115 
Arm length formula 2 > 4 = 1 or subequal 2 > 4 > 1 or subequal subequal 4 = 3 = 2 > 1 
Arm width 9.5 8.5 7.4 6.4 
Sucker diameter 8.3 9.3 7.4 4.5 
Sucker counts (L, R) 
 Hc 72 78 79 78 
 4 141, – 141, – 138, – 145, – 
Gill count (outer/inner demibranch) 8/–, 9/– c. 8–9, c. 8–9 9/9, 9/9 8/9, 9/9 
Stylet length 20 20.1 – – 
Ligula length 7.1 9.0 6.2 3.8 
Calamus length 3.2 4.0 3.7 2.5 
Terminal organ length 39.5 29.5 Submature 
Diverticulum length 30.6 16.7 Submature 
Spermatophore count 3, 1TO 3, 1TO Submature 
Spermatophore length 69 69 54 Submature 
Spermatophore width 3.7 3.8 3.2 Submature 
Spermatophore reservoir length 14 20.2 15.8 Submature 
Spermatophore cord whorls c. 8 c. 7–8 c.Submature 
Repository MNHN MNHN MNHN MNHN 
Catalogue number 3803 2108 2109 2109 
Status Holotype Paratype Paratype Paratype 
Sex Male Male Male Male 
Maturity Mature Mature Mature Submature 
Total length 238 210 171 + 170 
Total wet weight (g) 95.7 75.1 49.1 39.4 
Dorsal mantle length 51.1 44.4 46.7 41.2 
Ventral mantle length 39.0 37.7 33.7 26.1 
Mantle width 41.7 40.5 35.5 34.3 
Head width 32.6 31.4 28.2 24.9 
Funnel length 19.5 20.5 16.4 15.8 
Free funnel length 8.7 7.0 5.1 7.7 
Funnel organ length 
 Lateral limb 9.7 10.4 7.3 7.5 
 Medial limb 9.7 13.0 9.9 8.8 
Web depths (L, R) 
 A 25 19 25 18 
 B 32, 32 30, 25 30, d 24, 27 
 C d, 37 36, 35 29, d 29, 34 
 D 38, 35SpG 36, 34SpG d, d 35, 33SpG 
 E 31 31 25 
Web depth formula C = D > B = E > A C = D > B = E > A  C = D > B = E > A 
Arm lengths (L, R) 
 1 152, 160 143, d 118, d 90, 102 
 2 175, 163 154, 154 116d?, d 114, 114 
 3 d (L) d (L) 112 (L) 117 (L) 
 Hc (R) 127 113 99 
 4 161, 157 147, d d, d 106, 115 
Arm length formula 2 > 4 = 1 or subequal 2 > 4 > 1 or subequal subequal 4 = 3 = 2 > 1 
Arm width 9.5 8.5 7.4 6.4 
Sucker diameter 8.3 9.3 7.4 4.5 
Sucker counts (L, R) 
 Hc 72 78 79 78 
 4 141, – 141, – 138, – 145, – 
Gill count (outer/inner demibranch) 8/–, 9/– c. 8–9, c. 8–9 9/9, 9/9 8/9, 9/9 
Stylet length 20 20.1 – – 
Ligula length 7.1 9.0 6.2 3.8 
Calamus length 3.2 4.0 3.7 2.5 
Terminal organ length 39.5 29.5 Submature 
Diverticulum length 30.6 16.7 Submature 
Spermatophore count 3, 1TO 3, 1TO Submature 
Spermatophore length 69 69 54 Submature 
Spermatophore width 3.7 3.8 3.2 Submature 
Spermatophore reservoir length 14 20.2 15.8 Submature 
Spermatophore cord whorls c. 8 c. 7–8 c.Submature 

A–E, web sectors starting from dorsal sector; d, damaged/distorted; InD, indistinct; Hc, hectocotylized arm of male; L, left; R, right; n/a, not applicable; SpG, spermatophore groove; TO, terminal organ; +, arm tip missing; –, not measured.

Arms: moderate length, around 3 times ML (2.8-3.5 times ML); moderately robust, sub-cylindrical along length, tapering evenly to fine tips. Arm autotomy at base of arms absent. Dorsal arms slightly shorter in material examined, remainder subequal. Suckers in two rows. Three to five extremely enlarged suckers on all arms in mature males (to around 15–20% of ML: 16.2–20.9% in three mature males), at level of sixth to tenth proximal suckers (Fig. 4B). Up to 145 suckers on intact arms (only known for males, 138–145).

Webs of moderate depth (deepest webs 21.7–29.9% of longest arm in intact males). Lateral webs slightly deeper than other sectors, web formula typically C = D > B = E > A. Webs margins well developed on all arms, widened as paddle-like flares in distal quarter of normal arms, with extreme tips of arms free of web (Fig. 4C).

Third right arm of males hectocotylized. Modified arm relatively short, approximately 2.5 times ML (2.4–2.5 times ML in intact material) and 85% length of opposite arm in only male with both third arms undamaged. Ligula (Figs 1D, 4D) of small to moderate size (5.6 and 8.0% of arm length in two intact mature males), spoon to leaf-shaped with wide, open groove, floor with around 10–12 simple transverse creases. Calamus large and proud, around 50% of ligula length (44.4, 45.1, 59.7%). 72–79 suckers on hectocotylized arm.

Gills with 8–9 lamellae on both inner and outer demibranchs, plus terminal lamella.

Digestive tract (Fig. 2A): Anterior salivary glands of moderate size, c. 60% of length of buccal mass. Posterior salivary glands of moderate size, slightly larger than buccal mass (112% in 49.4 mm ML male, MNHN 2109), c. 50% of digestive gland length (49.2% in same specimen). Crop with distinct diverticulum. Stomach bipartite. Caecum coiled in single whorl, distinctly striated. Digestive gland roughly ovoid. Ink sac present, deeply embedded. Anal flaps present. Upper beak (Fig. 2B) with hooked rostrum and moderate hood (40.5% of upper beak length in same specimen). Lower beak with rounded rostrum, narrow hood and relatively parallel lateral walls separated in approximately posterior 15%, although pigmentation gives appearance of deeper fork (Fig. 2C, D). Radula with seven teeth and two marginal plates in each transverse row (Fig. 4E). Rhachidian tooth with two to three lateral cusps on each side of large medial cone. Lateral cusps in asymmetrical seriation, migrating from lateral to medial position over approximately seven transverse rows.

Figure 2.

Histoctopus discus n. gen., n. sp. AE. Digestive components of 46.7 mm ML male (MNHN 2109). A. Digestive tract. Abbreviations: af, anal flaps; asg, anterior salivary gland; bm, buccal mass; c, caecum; cd, crop diverticulum; cr, crop; dg, digestive gland; I, intestine; is, ink sac; o, oesophagus; psg, posterior salivary gland; s, stomach. B. Lateral view of upper beak. C. Lateral view of lower beak. D. Ventral view of lower beak. Scale bars: A = 10 mm; BD = 5 mm.

Figure 2.

Histoctopus discus n. gen., n. sp. AE. Digestive components of 46.7 mm ML male (MNHN 2109). A. Digestive tract. Abbreviations: af, anal flaps; asg, anterior salivary gland; bm, buccal mass; c, caecum; cd, crop diverticulum; cr, crop; dg, digestive gland; I, intestine; is, ink sac; o, oesophagus; psg, posterior salivary gland; s, stomach. B. Lateral view of upper beak. C. Lateral view of lower beak. D. Ventral view of lower beak. Scale bars: A = 10 mm; BD = 5 mm.

Male reproductive tract (Fig. 3A): Terminal organ (‘penis’) in mature male very large, around two-thirds of ML (66.4 and 77.3% in two undamaged mature males), T-shaped with diverticulum longer than distal portion. Spermatophore storage sac with unique darkly pigmented large glandular mass on posterior tip, termed here the ‘spermatophore storage gland’ (SSG, Fig. 3). Spermatophores: (Fig. 3B) large, longer than ML (54–69 mm, 1.2, 1.4 and 1.6 times ML), few (1–4). Sperm reservoir: wide (4.9, 5.1, 5.3% of length) short, under one-third of spermatophore length (20.3, 29.3, 29.3%). Sperm cord: robust double strand of around seven to nine loose coils. Ejaculatory apparatus simple, without coils. Central section of ejaculatory apparatus with regular ridged coils, potentially armed with small teeth (not distinct in material examined).

Figure 3.

Histoctopus discus n. gen., n. sp. A, B. Male reproductive system of 44.4 mm ML paratype (MNHN 2108). A. Reproductive tract. Abbreviations: a, appendix; as, accessory spermatophoric gland; mg, mucilagenous gland; sg, spermatophoric gland; ss, spermatophore storage sac; ssg, spermatophore sac gland; t, testes; to, terminal organ; vd, vas deferens. B. Spermatophore. Inset: oral cap end of spermatophore. Abbreviation: sr, sperm reservoir. Scale bars: A = 10 mm; B = 10 mm (inset 2 mm).

Figure 3.

Histoctopus discus n. gen., n. sp. A, B. Male reproductive system of 44.4 mm ML paratype (MNHN 2108). A. Reproductive tract. Abbreviations: a, appendix; as, accessory spermatophoric gland; mg, mucilagenous gland; sg, spermatophoric gland; ss, spermatophore storage sac; ssg, spermatophore sac gland; t, testes; to, terminal organ; vd, vas deferens. B. Spermatophore. Inset: oral cap end of spermatophore. Abbreviation: sr, sperm reservoir. Scale bars: A = 10 mm; B = 10 mm (inset 2 mm).

Female material unknown.

Basal colour of preserved specimens typically orange brown dorsally and cream ventrally. Orange-brown colour over eyes with blue-black subdermal colour. Four darker brown patches on dorsal mantle behind head as pairs separated by strip of cream-coloured papillae (Fig. 1A). Aboral web sectors A, B and C dark red brown, darker colour not extending onto aboral arms or lateral web extensions. Small dark chromatophores evenly scattered amongst papillae over all dorsal surfaces. Small founder chromatophores widely scattered on anterior half of ventral mantle.

Skin sculptured with evenly spaced, small rounded papillae forming low granular texture over all surfaces (Fig. 4A). No enlarged papillae evident over eyes. Single, slightly larger papilla on posterior tip of mantle, often white in colour. Papillae texture pronounced above eyes. Lateral ridge absent.

Figure 4.

Histoctopus discus n. gen., n. sp. A. Left dorso-lateral view of whole animal, 46.7 mm ML male paratype (MNHN 2109). B. Enlarged suckers of 44.4 mm ML male paratype (MNHN 2108). C. Close-up of web margins on arms 2 and 3, 46.7 mm ML male paratype (MNHN 2109). D. Hectocotylus of 51.5 mm ML male holotype (MNHN 3803). E. Radula from 46.7 mm ML male paratype (MNHN 2109). Scale bar E = 0.5 mm. (This figure appears in colour in the online version of Journal of Molluscan Studies.)

Figure 4.

Histoctopus discus n. gen., n. sp. A. Left dorso-lateral view of whole animal, 46.7 mm ML male paratype (MNHN 2109). B. Enlarged suckers of 44.4 mm ML male paratype (MNHN 2108). C. Close-up of web margins on arms 2 and 3, 46.7 mm ML male paratype (MNHN 2109). D. Hectocotylus of 51.5 mm ML male holotype (MNHN 3803). E. Radula from 46.7 mm ML male paratype (MNHN 2109). Scale bar E = 0.5 mm. (This figure appears in colour in the online version of Journal of Molluscan Studies.)

Skin colour and sculpture of live animal unknown.

Life history: Nothing is known of the biology of this species. The extreme sucker enlargement found in this species suggests some special use in courtship behaviour (see Discussion).

Distribution: Southwest Pacific Ocean; only known from Sponge Bank, Norfolk Ridge, south of New Caledonia. Collected at depths of 500 to 545 m.

Remarks: See below.

Histoctopus zipkasae new species
(Figs 5–8)

Type material: Holotype: Western Australia, Northwest Shelf: 1M: 61.6 mm ML, MV F164025, FRV ‘Soela’, SO1/84/18, 18°44′S, 117°00′E, 404 m, coll. CSIRO, 30 Jan 1984. Paratypes: Western Australia, Northwest Shelf: 1M, 54.6 mm ML, MV F164024, FV Surefire, SF1/88/02, 18°25′S, 117°48′E, 375 m, 0700–1000 h, coll. CSIRO, 21 Aug 1988. 1M, 58.5, 2F, 36.5, 71.1 mm ML, MV F164034, FV Surefire, SF1/88, 17°45′S, 118°32′E, 420 m, 1000–1300 h, coll. CSIRO, 27 Aug 1988. 1M, 62.7 mm ML, MV F164031, FV Courageous, CR1/89/03, 18°33′S, 117°53′E, 380 m, 1305 h, coll. CSIRO, 8 Feb 1989. 1F: 69.4 mm ML, MV F164035, FRV Soela, SO1/84/12, 18°53′S, 116°10′E, 458 m, coll. CSIRO, 29 Jan 1984. 1M, 73.8 mm ML, MV F164020, FV Striker, shot 1, 16°59′S, 120°10′E, 411 m, 0200–0700 h, coll. Sue Morris, CSIRO, 3 Apr 1989. 2F, 89.3, 107.7 mm ML, MV F164036, FRV Soela, SO4/82, 18°01′S, 118°23′E, 376 m, 2030 h, coll. CSIRO, 1 Aug 1982.

Other material examined: Western Australia, Northwest Shelf: 1F, 53.7 mm ML, MV F164033, FV Surefire, SF1/88/02, 18°25′S, 117°48′E, 375 m, 0700–1000 h, coll. CSIRO, 21 Aug 1988. 1F, 70.8 mm ML, MV F164082, FV Surefire, SF1/88, 18°36′S, 117°20′E, 425 m, 1215–1515 h, coll. CSIRO, 20 Aug 1988. 1F, 72.0, mm ML, MV F164032, FV Surefire, SF1/88, 18°35.8′S, 117°20′E, 428 m, 1700–2000 h, coll. CSIRO, 20 Aug 1988.

Remote video still images: Western Australia: Off Kalbarri, 27°56.58′S, 113°05.18′E, RV Southern Surveyor, SS07/2005/96, 424 m, 01:27 h, image coll. CSIRO, 30 July 2005, data ID: 45922. Off Abrolhos Islands, 29°01.23′S, 113°47.32′E, RV Southern Surveyor, SS07/2005/107, 384 m, 06:46 h, image coll. CSIRO, 31 July 2005, data ID: 56337. Off Abrolhos Islands, 29°01.35′S, 113°47.31′E, RV Southern Surveyor, SS07/2005/107, 415 m, 06:51 h, image coll. CSIRO, 31 July 2005, data ID: 56629. Off Jurien Bay, 29°50.88′S, 114°22.02′E RV Southern Surveyor, SS07/2005/125, 401 m, 02:15 h, image coll. CSIRO, 2 Aug 2005, data ID: 67222. Perth Canyon, 32°00.19S, 115°11.29′E, RV Southern Surveyor, SS07/2005/217, 449 m, 00:47 h, image coll. CSIRO, 2 Aug 2005, data ID: 120359.

Etymology: zipkasae, after the senior author's wonderful wife, Karen Zipkas.

Diagnosis: Medium-sized species, ML to at least 107 mm. Arm lengths approximately three times ML (longest 2.4–3.7 × ML). Arms approximately equal in length, dorsal arms slightly shorter. Web sectors very thin and membranous, deep, up to 30% of longest arm length. Webs approximately equal in depth, lateral webs slightly deeper. Webs extend as membranous flared margins along entire length of arms, very well developed towards arm tips. Suckers forming two rows. Sucker counts to around 168 on normal arms. Hectocotylized arm with 66–68 suckers. Two to three slightly to moderately enlarged and flattened suckers present on all arms of mature males, diameter up to 15% of ML at level of 7th to 13th proximal sucker. Large W-shaped funnel organ. Gill count nine lamellae per demibranch. Ink sac and anal flaps present. Third right arm hectocotylized. Ligula small to moderate size (4.5–6.2% of arm length), spoon-shaped with robust rims and wide, open groove, floor with around 10–12 simple transverse creases. Calamus large and prominent, 34.7–59.7%. Spermatophores large (0.9–1.1 × ML) and few (3–8). Distal oviducts thickened along length. Eggs of moderate size (6.5–7.8 mm, 7.2–9.1% ML). Colour pattern: Pink orange dorsally, cream ventrally. Orange-brown basal colour on first three arm pairs. Two transverse rows of small white spots on dorsal mantle. Regularly spaced white spots present along aboral midline of first three arm pairs. Skin sculpture: Small, round papillae uniformly scattered on all dorsal surfaces; larger supraocular papillae absent. Lateral mantle ridge absent.

Description: The following description is based on five mature males and five females (three mature, two submature). Counts and measurements are presented in Tables 3 and 4.

Table 3.

Histoctopus zipkasae n. gen., n. sp.: counts and measurements (mm) of male material.

Repository MV MV MV MV MV 
Catalogue number F164025 F164020 F164031 F164024 F164034 
Status Holotype Paratype Paratype Paratype Paratype 
Maturity Mature Mature Mature Mature Mature 
Total length 278 291 265 272 
Total wet weight (g) 136 89 83 60 79 
Dorsal mantle length 61.6 73.8 62.7 54.6 58.5 
Ventral mantle length 50.2 58.5 51.0 50.6 52.2 
Mantle width 47.8 46.8 39.7 42.6 
Head width 32.9 26.6 29.9 30.4 
Funnel length 22.0 25.3 23.8 20.7 
Free funnel length 7.2 11.1 5.4 6.5 
Funnel organ length      
 lateral limb 9.2 InD InD InD 
 medial limb 10.3 InD InD InD 
Web depths (L, R) 
 A 25 28 34 
 B d, d 39, 39 d, d d, 35 d, d 
 C 38, d 39, 43 d, d d, 32 33, d 
 D 43, d d, 38SpG d, d 30, d 35, 31 
 E 30 33 30 29 
Web depth formula D > B > E > A C = B > E > A E > D > C 
Arm lengths (L, R) 
 1 d, 196 164, d d, d 196, 197 d, d 
 2 168, 200 188, 198 d, d 200, d d, d 
 3 138 (L) d (L) d (L) 148 (L) d (L) 
 Hc (R) 118 123 117 106 
 4 178, 186 171, 172 d, d 169, 160 d, 193 
Arm length formula 2 = 1 > 4 > 3? 2 > 4 > 1 1 = 2 > 4 > 3 
Arm width 10.0 8.6 8.7 7.8 9.4 
Sucker diameter 7.2 7.0 5.0 4.3 8.8 
Sucker counts (L, R) 
 1 – – – – – 
 2 –, 157 – – 152, – – 
 3 – – – – – 
 Hc 68 67 67 66 
 4 – –, c. 150 – – –, 149 
Gill count (outer/inner demibranch) 9/9, 9/9 c. 9, c.c. 9, c.9/?, 9/? c. 9, c.
Stylet length 20.4 21.2 21.2 19.6 21.1 
Ligula length 8.5 7.2 7.2 4.8 
Calamus length 5.0 2.5 4.3 2.3 
Terminal organ length 28.4 39.2 33.3 30.7 
Diverticulum length 19.0 – 
Spermatophore count 5, 1TO 4, 1TO 2, 1TO 2, 1TO 7, 1TO 
Spermatophore length c. 70 68 58 
Spermatophore width 3.4 3.5 3.0 3.1 
Spermatophore reservoir length c. 20 14 13.2 
Spermatophore cord whorls ∼6 c. 5 + 
Repository MV MV MV MV MV 
Catalogue number F164025 F164020 F164031 F164024 F164034 
Status Holotype Paratype Paratype Paratype Paratype 
Maturity Mature Mature Mature Mature Mature 
Total length 278 291 265 272 
Total wet weight (g) 136 89 83 60 79 
Dorsal mantle length 61.6 73.8 62.7 54.6 58.5 
Ventral mantle length 50.2 58.5 51.0 50.6 52.2 
Mantle width 47.8 46.8 39.7 42.6 
Head width 32.9 26.6 29.9 30.4 
Funnel length 22.0 25.3 23.8 20.7 
Free funnel length 7.2 11.1 5.4 6.5 
Funnel organ length      
 lateral limb 9.2 InD InD InD 
 medial limb 10.3 InD InD InD 
Web depths (L, R) 
 A 25 28 34 
 B d, d 39, 39 d, d d, 35 d, d 
 C 38, d 39, 43 d, d d, 32 33, d 
 D 43, d d, 38SpG d, d 30, d 35, 31 
 E 30 33 30 29 
Web depth formula D > B > E > A C = B > E > A E > D > C 
Arm lengths (L, R) 
 1 d, 196 164, d d, d 196, 197 d, d 
 2 168, 200 188, 198 d, d 200, d d, d 
 3 138 (L) d (L) d (L) 148 (L) d (L) 
 Hc (R) 118 123 117 106 
 4 178, 186 171, 172 d, d 169, 160 d, 193 
Arm length formula 2 = 1 > 4 > 3? 2 > 4 > 1 1 = 2 > 4 > 3 
Arm width 10.0 8.6 8.7 7.8 9.4 
Sucker diameter 7.2 7.0 5.0 4.3 8.8 
Sucker counts (L, R) 
 1 – – – – – 
 2 –, 157 – – 152, – – 
 3 – – – – – 
 Hc 68 67 67 66 
 4 – –, c. 150 – – –, 149 
Gill count (outer/inner demibranch) 9/9, 9/9 c. 9, c.c. 9, c.9/?, 9/? c. 9, c.
Stylet length 20.4 21.2 21.2 19.6 21.1 
Ligula length 8.5 7.2 7.2 4.8 
Calamus length 5.0 2.5 4.3 2.3 
Terminal organ length 28.4 39.2 33.3 30.7 
Diverticulum length 19.0 – 
Spermatophore count 5, 1TO 4, 1TO 2, 1TO 2, 1TO 7, 1TO 
Spermatophore length c. 70 68 58 
Spermatophore width 3.4 3.5 3.0 3.1 
Spermatophore reservoir length c. 20 14 13.2 
Spermatophore cord whorls ∼6 c. 5 + 

A–E, web sectors starting from dorsal sector; d, damaged/distorted; InD, indistinct; Hc, hectocotylized arm of male; L, left; R, right; n/a, not applicable; SpG, spermatophore groove; TO, terminal organ; –, not measured.

Table 4.

Histoctopus zipkasae n. gen., n. sp.: counts and measurements (mm) of female material.

Repository MV MV MV MV MV 
Catalogue number F164036 F164036 F164034 F164028 F164035 
Status Paratype Paratype Paratype – Paratype 
Maturity Gravid Gravid Gravid Submature Submature 
Total length 383 386 310 347 240 
Total wet weight (g) 243 206 132 133 114 
Dorsal mantle length 107.7 89.3 71.1 70.8 69.4 
Ventral mantle length 86.9 74.0 59.8 55.2 58.3 
Mantle width 62.8 58.0 47.8 50.1 48.3 
Head width 38.6 40.2 30.1 34.1 37.5 
Funnel length 34.0 34.5 25.9 23.6 
Free funnel length 11.5 17.4 11.5 5.5 
Funnel organ length 
 Lateral limb InD InD InD InD 11.2 
 Medial limb InD InD InD InD 13.3 
Web depths (L, R) 
 A 42 36 30 30 28 
 B d, d 57, 59 34, 39 35, 45 32, 47 
 C d, 53 57, 62 45, 47 39, 45 48, 48 
 D d, 50 57, d d, d 39, 39 45, d 
 E 33 32 
Web depth formula C = D > A B = C = D > A C > B > A B = C = D > E > A B = C > D > E > A 
Arm lengths (L, R) 
 1 d, 258 214, 207 d, d 173, 178 153, d 
 2 225, 255 d, 274 222, d 220, 257 167, 157 
 3 225, d 233, 219 208, d 191, d d, 150 
 4 205, 240 d, d d, 215 237, 225 d, 167 
Arm length formula 1 = 2 > 4 > 3 2 > 3 > 1 4 = 3 = 2 2 = 3 > 1 4 = 2 > 3 = 1 
Arm width 11.2 11.1 9.5 11.3 10.8 
Sucker diameter 4.3 5.5 5.3 5.6 4.8 
Sucker counts (L, R) 
 1 – – – – – 
 2 – – 165, – –, 160 168, – 
 3 164, – –, c. 153 166, – – – 
 4 – – – – – 
Gill count (outer/inner demibranch) 9/?, 9/? InD, InD 9/9, 9/9 ?/9, 9/? 9/?, 9/? 
Stylet length 29.7 26.5 – – – 
Egg length 7.8 6.5 6.5 Submature Submature 
Egg width 1.7 1.8 1.8 Submature Submature 
Repository MV MV MV MV MV 
Catalogue number F164036 F164036 F164034 F164028 F164035 
Status Paratype Paratype Paratype – Paratype 
Maturity Gravid Gravid Gravid Submature Submature 
Total length 383 386 310 347 240 
Total wet weight (g) 243 206 132 133 114 
Dorsal mantle length 107.7 89.3 71.1 70.8 69.4 
Ventral mantle length 86.9 74.0 59.8 55.2 58.3 
Mantle width 62.8 58.0 47.8 50.1 48.3 
Head width 38.6 40.2 30.1 34.1 37.5 
Funnel length 34.0 34.5 25.9 23.6 
Free funnel length 11.5 17.4 11.5 5.5 
Funnel organ length 
 Lateral limb InD InD InD InD 11.2 
 Medial limb InD InD InD InD 13.3 
Web depths (L, R) 
 A 42 36 30 30 28 
 B d, d 57, 59 34, 39 35, 45 32, 47 
 C d, 53 57, 62 45, 47 39, 45 48, 48 
 D d, 50 57, d d, d 39, 39 45, d 
 E 33 32 
Web depth formula C = D > A B = C = D > A C > B > A B = C = D > E > A B = C > D > E > A 
Arm lengths (L, R) 
 1 d, 258 214, 207 d, d 173, 178 153, d 
 2 225, 255 d, 274 222, d 220, 257 167, 157 
 3 225, d 233, 219 208, d 191, d d, 150 
 4 205, 240 d, d d, 215 237, 225 d, 167 
Arm length formula 1 = 2 > 4 > 3 2 > 3 > 1 4 = 3 = 2 2 = 3 > 1 4 = 2 > 3 = 1 
Arm width 11.2 11.1 9.5 11.3 10.8 
Sucker diameter 4.3 5.5 5.3 5.6 4.8 
Sucker counts (L, R) 
 1 – – – – – 
 2 – – 165, – –, 160 168, – 
 3 164, – –, c. 153 166, – – – 
 4 – – – – – 
Gill count (outer/inner demibranch) 9/?, 9/? InD, InD 9/9, 9/9 ?/9, 9/? 9/?, 9/? 
Stylet length 29.7 26.5 – – – 
Egg length 7.8 6.5 6.5 Submature Submature 
Egg width 1.7 1.8 1.8 Submature Submature 

A–E, web sectors starting from dorsal sector; d, damaged/distorted; InD, indistinct; L, left; R, right; n/a, not applicable; –, not measured.

Medium-size muscular species (Figs 5A, 8A); ML to at least 107 mm, total length to at least 383 mm; weight to at least 243 g. Mantle elongate ovoid, longer than wide (width 58.3–67.0–77.6% of ML). Head wide (35.8–46.0–54.0% of ML; 56.8–68.0–77.6% of mantle width). Skin firm, sculptured and pigmented. Eyes large. Stylets: large, robust rods, mineralised in some specimens (Fig. 5B), length around 30% of ML (28–36% of ML in seven specimens). Mantle opening wide, c. 50% of circumference of body at level of opening. Funnel: moderate length, c. 35% of ML (31.6–35.5–38.6% of ML), free portion moderate to long, c. 35% of funnel length (22.7–35.9–50.4%). Funnel organ: W-shaped (Fig. 5C), lateral limbs slightly shorter than median ones (lateral limbs 84.2, 89.3% of median limbs in 69.4 mm ML female and 61.6 mm ML male, respectively); occupies c. 50% of funnel length (46.8, 56.3% in 61.6 mm ML male and 69.4 mm ML female, respectively).

Figure 5.

Histoctopus zipkasae n. gen., n. sp. AD. 61.6.mm ML male holotype (MV F164025). A. Dorsal whole animal. B. Stylet. C. Funnel organ. D. Ligula. Scale bars: A = 50 mm; BD = 5 mm.

Figure 5.

Histoctopus zipkasae n. gen., n. sp. AD. 61.6.mm ML male holotype (MV F164025). A. Dorsal whole animal. B. Stylet. C. Funnel organ. D. Ligula. Scale bars: A = 50 mm; BD = 5 mm.

Arms: moderate length, around three times ML (2.4–3.7 times ML); moderately robust, sub-cylindrical along length, tapering evenly to fine tips. Arm autotomy at base of arms absent. Dorsal arms typically slightly shorter, remainder subequal. Suckers in two rows. Two to three slightly to moderately enlarged suckers on all arms in males (to around 15% of ML: 8.0–15.0% in five mature males), at level of 7th to 13th proximal suckers (Fig. 8B). Up to 168 suckers on intact arms (males 149–157, females 160–168).

Webs of moderate depth (deepest webs 18–29% of longest arm in intact material). Lateral webs slightly deeper than other sectors, web formula typically B = C = D > E > A. Webs margins well developed on all arms, running as wide flange along length of arms (Fig. 8A).

Third right arm of males hectocotylized. Modified arm relatively short, c. 1.8 times ML (1.7–1.9 times ML in intact material) and 80% length of opposite arm (71.6, 85.8% in two males with both third arms undamaged). Ligula (Figs 5D, 8C, D) of small to moderate size (4.5–6.2% of arm length in four intact mature males), spoon-shaped with robust rims and wide, open groove, floor with around 10–12 simple transverse creases. Calamus large and proud, 34.7–59.7% in material examined. A total of 66–68 suckers on hectocotylized arm. Web lateral margin extension also present on hectocotylized arm (third right), displacing spermatophore groove away from arm face (Fig. 8A, D).

Gills with nine lamellae on both inner and outer demibranchs, plus terminal lamella.

Digestive tract (Fig. 6A): Anterior salivary glands: moderate to small, c. 30% of length of buccal mass. Posterior salivary glands of moderate size, approximately equal in length with buccal mass (101% in 62.7 mm ML male, MV F164031), c. 50% of digestive gland length (49.2% in same specimen). Crop with distinct diverticulum. Stomach bipartite. Caecum coiled in single whorl, distinctly striated. Digestive gland roughly ovoid. Ink sac present, deeply embedded. Anal flaps present. Upper beak (Fig. 6B) with hooked rostrum and moderate hood (40% of upper beak length in same specimen). Lower beak with rounded rostrum, narrow hood and relatively parallel lateral walls separated in approximately posterior 15%, although pigmentation gives appearance of deeper fork (Fig. 6C, D). Radula with seven teeth and two marginal plates in each transverse row (Fig. 6E, F). Rhachidian tooth with two lateral cusps, sometimes three, on each side of large medial cone. Lateral cusps in asymmetrical seriation, migrating from lateral to medial position over c. 7 transverse rows.

Figure 6.

Histoctopus zipkasae n. gen., n. sp. A.F. Digestive components of 62.7 mm ML male (MV F164031). A. Digestive tract. Abbreviations as in Figure 2 plus p, pancreatic tissue. B. Lateral view of upper beak. C. Lateral view of lower beak. D. Ventral view of lower beak. E., F. Radula. Scale bars: A = 10 mm; BD = 5 mm; E, F = 1 mm.

Figure 6.

Histoctopus zipkasae n. gen., n. sp. A.F. Digestive components of 62.7 mm ML male (MV F164031). A. Digestive tract. Abbreviations as in Figure 2 plus p, pancreatic tissue. B. Lateral view of upper beak. C. Lateral view of lower beak. D. Ventral view of lower beak. E., F. Radula. Scale bars: A = 10 mm; BD = 5 mm; E, F = 1 mm.

Male reproductive tract (Fig. 7A): Terminal organ (‘penis’) in mature male very large, around half ML (46.1–61.0% in four undamaged mature males), T-shaped with diverticulum longer than distal portion. Spermatophore storage sac with darkly pigmented large glandular mass on posterior tip. Spermatophores (Fig. 7B) large, approximately equal in length with mantle (58–70 mm, 0.9–1.1 × ML), few (3–8). Sperm reservoir: under one-third of spermatophore length (20.6, 22.8, 28.6%). Sperm cord: robust double strand of around six loose coils. Ejaculatory apparatus simple without coils.

Figure 7.

Histoctopus zipkasae n. gen., n. sp. A. Reproductive tract of 61.6 mm ML holotype (MV F164025). Abbreviations as in Figure 3.B. Spermatophore of 73.8 mm ML male (MV F164020). Abbreviation: SR, sperm reservoir. C. Female reproductive tract of 89.3 mm ML paratype (MV F164036). Abbreviations: do, distal oviduct; o, ovary; og, oviducal gland; po, proximal oviduct. Scale bars: A = 10 mm; B = 5 mm; C = 10 mm.

Figure 7.

Histoctopus zipkasae n. gen., n. sp. A. Reproductive tract of 61.6 mm ML holotype (MV F164025). Abbreviations as in Figure 3.B. Spermatophore of 73.8 mm ML male (MV F164020). Abbreviation: SR, sperm reservoir. C. Female reproductive tract of 89.3 mm ML paratype (MV F164036). Abbreviations: do, distal oviduct; o, ovary; og, oviducal gland; po, proximal oviduct. Scale bars: A = 10 mm; B = 5 mm; C = 10 mm.

Female reproductive tract illustrated in Figure 7C. Distal oviducts thickened along length, with openings high in mantle cavity, level with posterior attachment of medial pallial septum. Oviducal glands: dark, without obvious subdivisions. Eggs of moderate size relative to ML (6.5–7.8 mm in three gravid females, 7.2–9.1% ML). Hatchlings unknown.

Video footage of live individuals of this species was obtained by CSIRO on board the RV Southern Surveyor in 2005 (e.g. video still image Fig. 8E). Live animals have an orange-brown arm crown, a pink-orange mantle and the two transverse rows of small white spots that are evident in preserved material. Raised papillae are scattered over the dorsal and lateral mantle. Expanded web margins appear retracted in active animal (Fig. 8E).

Figure 8.

Histoctopus zipkasae n. gen., n. sp. AD. 61.6 mm ML male holotype (MV F164025). A. Left lateral view of whole animal. B. Oral view of arm crown showing slightly enlarged suckers (arrows). C, D. Hectocotylus. E. Live animal image from CSIRO tow camera, 401 m, off Jurien Bay, Western Australia, photo: B. Barker, CSIRO.

Figure 8.

Histoctopus zipkasae n. gen., n. sp. AD. 61.6 mm ML male holotype (MV F164025). A. Left lateral view of whole animal. B. Oral view of arm crown showing slightly enlarged suckers (arrows). C, D. Hectocotylus. E. Live animal image from CSIRO tow camera, 401 m, off Jurien Bay, Western Australia, photo: B. Barker, CSIRO.

Basal colour of preserved specimens typically cream. Orange-brown colour over eyes with blue-black subdermal colour visible in some specimens. Small dark chromatophores evenly scattered amongst papillae over all dorsal surfaces.

Skin sculptured with evenly spaced small rounded papillae forming low granular texture over all surfaces (Fig. 8A). Low papillae texture pronounced above eyes but none distinctly enlarged. Lateral mantle ridge absent.

Life history: The live animals were photographed in 2005 (Fig. 8E) on fine sand/silt and on low rocky rubble. All animals were photographed between 00:47 and 06:51 h, suggesting primarily nocturnal to crepuscular activity patterns. Three of the five live images of this species show animals jet escaping, presumably away from the ROV and lights. Nothing else is known of behaviour or biology.

Distribution: Indian Ocean, off Western Australia from Perth Canyon to Northwest Shelf (Fig. 9), trawled at depths of 375–458 m. Video records from 384–449 m.

Figure 9.

Known distribution for the genus Histoctopus n. gen. Symbols: circle, H. zipkasae material examined; triangle, H. zipkasae video records; square, H. discus material examined.

Figure 9.

Known distribution for the genus Histoctopus n. gen. Symbols: circle, H. zipkasae material examined; triangle, H. zipkasae video records; square, H. discus material examined.

Remarks: Histoctopus zipkasae is distinguished from Histoctopus discus in that it is larger (to 107 mm vs 51 mm in H. discus), has higher sucker counts on the normal arms (149–168 vs 138–145) yet lower sucker counts on the hectocotylized arm (66–68 vs 72–79), shorter hectocotylized arm relative to ML (1.7–1.9 × ML vs 2.4–2.5), smaller enlarged suckers (to 15 vs to 20%), and smaller spermatophores relative to ML (0.9–1.1 × ML vs 1.2–1.6). See summary in Table 5.

Table 5.

Morphological comparison of new Histoctopus species.

 H. discus H. zipkasae 
Maximum size (mm ML) 51 107 
Arm length ( × ML) 2.8–3 2.4–3.7 
Sucker count 138–145 149–168 
Hectocotylized arm sucker count 72–79 66–68 
Enlarged suckers on all arms of males 3–5, very large 2–3, slightly enlarged 
Enlarged sucker size (% ML) 16–21 8–15 
Hectocotylized arm length (×ML) 2.4–2.5 1.7–1.9 
Ligula length (% HAL) 5.6, 8.0 4.5–6.2 
Calamus length (% LL) 44–60 35–60 
Spermatophore length 54–69 58–70 
Spermatophore length (×ML) 1.2–1.6 0.9–1.1 
 H. discus H. zipkasae 
Maximum size (mm ML) 51 107 
Arm length ( × ML) 2.8–3 2.4–3.7 
Sucker count 138–145 149–168 
Hectocotylized arm sucker count 72–79 66–68 
Enlarged suckers on all arms of males 3–5, very large 2–3, slightly enlarged 
Enlarged sucker size (% ML) 16–21 8–15 
Hectocotylized arm length (×ML) 2.4–2.5 1.7–1.9 
Ligula length (% HAL) 5.6, 8.0 4.5–6.2 
Calamus length (% LL) 44–60 35–60 
Spermatophore length 54–69 58–70 
Spermatophore length (×ML) 1.2–1.6 0.9–1.1 

ML, mantle length; HAL, hectocotylized arm length; LL, ligula length.

DISCUSSION

The new genus and its two new species described here were collected on the continental slope and seamounts at depths of between 375 and 545 m. Of all the benthic octopuses in the world, the distinctive form of flared distal web margins found in Histoctopus species is reported in only three other octopus genera, Velodona (Fig. 10A), Pteroctopus (Fig. 10B–D) and Graneledone (G. antarctica in Vecchione, Allcock & Piatkowski, 2005). The first two taxa occur in comparable depths to Histoctopus, typically 200–750 m. The third occurs to depths of more than 2000 m (Voss, 1976). The function of these distal web margin expansions is unknown but may be associated with feeding and/or locomotion.

Figure 10.

Other octopodid genera with flared distal web margins. A.Velodona togata, whole animal, South Africa Museum, Cape Town. BD.Pteroctopus sp., Muséum National d'Histoire Naturelle, Paris, B. Whole animal. C. Distal arm tip. D. Hectocotylized arm. (This figure appears in colour in the online version of Journal of Molluscan Studies.)

Figure 10.

Other octopodid genera with flared distal web margins. A.Velodona togata, whole animal, South Africa Museum, Cape Town. BD.Pteroctopus sp., Muséum National d'Histoire Naturelle, Paris, B. Whole animal. C. Distal arm tip. D. Hectocotylized arm. (This figure appears in colour in the online version of Journal of Molluscan Studies.)

Many shallow-water octopuses use proximal web sectors to ensnare prey by enveloping boulders or small coral heads and using the arm tips to flush prey into the webs and waiting suckers. Octopus cyanea and Octopus maorum use such techniques (Norman, 2000). Similar techniques are used by other octopus species to capture small prey (i.e. Wunderpus photogenicus, Hochberg et al., 2006; Vulcanoctopus hydrothermalis, Voight, 2005). The flared distal web margins with free distal arm tips in Histoctopus, Velodona and Pteroctopus may be used to forage for and snare prey while extending the arms over areas of soft sediment.

An alternative hypothesis is that the extreme web development in these three mid-depth genera relates to swimming behaviour. These flared webs may provide lift to the arms while jet swimming, potentially for energy efficient swimming. Until live observations are made of all three genera, these suggestions remain speculative.

Sucker enlargement found in mature males of Histoctopus, particularly the extreme enlargement in H. discus, is unusual. The presence of enlarged suckers only in males suggests a reproductive function for these modified suckers. Packard (1961) reported that enlarged suckers in mature males of the shallow-water species, Octopus vulgaris, were used for visual displays as a signal to females of state of maturity and cues for mating. With poor light penetration at depth (the two known members of Histoctopus occurring at 375–545 m), enlarged suckers are less likely to function as visual reproductive cues. Instead, these larger suckers may act as tactile [or even chemosensory, Voight (1991)] indicators of sexual identity and maturity.

The genus Histoctopus is described here based on two species from comparable depths in Western Australia and a seamount south of New Caledonia. Norman et al. (2005) reported regional endemism at parallel latitudes and depths for five species of the genus Scaeurgus in the area surrounding New Caledonia [Scaeurgus spp.: 19–25°S latitude, depth: 230–530 m; Histoctopus spp. 18–19°S (Western Australia), c. 25°S (New Caledonia), depth: 375–545 m]. Norman et al. (2005) also reported undescribed Scaeurgus species from off the Western Australian coast. Biogeographic links between the Western Australian continental slope and New Caledonian seamounts merit further investigation. It is possible that these taxa share palaeo-austral origins and affinities.

ACKNOWLEDGEMENTS

The authors wish to thank the researchers who collected and carefully preserved the material reported here, particularly Bertrand Richer de Forges, Philippe Bouchet and the staff of ORSTOM and CSIRO. The first and third authors also wish to acknowledge the financial support of the Muséum national d'Histoire naturelle on repeat visits to Paris to examine the extensive deep-water cephalopod collections housed in this museum. Warm thanks also to Guy Boucher for kind hospitality during these visits. Thanks to Joan Clarke of Department of Zoology, University of Melbourne, for SEM assistance; Franzis Althaus, Bruce Barker and Karen Gowlett-Holmes of CSIRO for provision of live images of H. zipkasae from deep-water camera deployments in Western Australia through the ‘Voyage of Discovery, CSIRO Wealth from Oceans Flagship’ programme. Thanks also to Louise Allcock, Janet Voight and an anonymous reviewer for constructive and helpful reviews of this paper.

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