The sound of a snail: two cases of acoustic defence in gastropods

Extract

Sound production has evolved independently in many phyla over time (Senter, 2008). Many animals produce sounds for communication, either with congeners or in reaction to predators (for examples of the latter in invertebrates see Bura, Fleming & Yack, 2009; Olofsson, Jakobsson & Wiklund, 2012), but Vermeij (2010) noted that deliberate production of acoustic signals is entirely unknown in the phylum Mollusca. However, Braun (1887) was the first to report briefly about the sound-producing snail Cantareus apertus (Born, 1778). He wrote “Es ist allgemein bekannt [sic], dass namentlich die grösseren Helices dadurch erzeugen, dass die in Lufthöhle angesammelte Luft aus dem Athemloch herausgestossen wird; gewöhnlich wird eine geringe Menge Schleim in kleine Blasen dabei aufgetrieben, deren Platzen das Geräusch vermehrt” [It is well known that especially the larger helices generate noise as the air in the pulmonary cavity is expelled through the pneumostome; usually a small amount of mucus is extruded and the bursting of small bubbles increases the sound]. This species was also mentioned by Caziot (1914), together with references to sounds produced during locomotion by other helicids and some limacid slugs (Vlès, 1908, 1909; Jousseaume, 1909). However, C. apertus makes the noise when resting, its shell rocking back and forth (see video by Wenger, 2014); the sounds produced by this species are made in the context of antipredator defence behaviour, after the shell has been touched suddenly. In terrestrial gastropods retraction into the shell is an important defence mechanism, usually accomplished while the aperture is facing down on the locomotion surface. In addition to this passive mode of defence, secretions from the skin and mucus glands can deter predatory attacks, due to the distasteful and deterrent compounds they may contain (reviewed for marine molluscs by Derby, 2007; see Pakarinen, 1994, and Mair & Port, 2002, for terrestrial examples). The topic of sound production in (land) snails seems to have been largely neglected since the paper by Caziot (1914), except for the mention by Fechter & Falkner (1990: 244–245) of the common name ‘Grunzschnecke’ (grunting snail) for C. apertus and the remark by Vermeij (2010).