Gigantopelta, Chen & Linse & Roterman & Copley & Rogers, 2015

Chen, Chong, Linse, Katrin, Roterman, Christopher N., Copley, Jonathan T. & Rogers, Alex D., 2015, A new genus of large hydrothermal vent-endemic gastropod (Neomphalina: Peltospiridae), Zoological Journal of the Linnean Society (Zool. J. Linn. Soc.) 175 (2), pp. 319-335 : 322-323

GIGANTOPELTA GEN. NOV.

Type species

Gigantopelta chessoia sp. nov., by original designation.

Etymology

Giganteus (Latin), gigantic; Pelta (Latin), shield. This refers to the extremely large adult shell size of the species in this genus for the family Peltospiridae . The genus name is feminine.

Zoobank registration urn:lsid:zoobank.org:act:C25960CA-B974-452C-AE24-B128FF1CEA0F

Diagnosis

Shell extremely large for family, reaching 45 mm in adult shell length. Shell globose, rather loosely coiled with deep suture, three to four whorls. Spire depressed. Protoconch consisting of 0.5 whorls. Aperture very large, circular, expanding rapidly. Thick, dark olive periostracum enveloping edge of aperture. Shell milky white and thin, not nacreous. Columellar folds lacking. Concentric, multispiral operculum present. Foot large. Cephalic tentacles thick, broad, triangular, thinning towards tips. Eyes lacking. Snout tapering and thick. Oesophageal gland hypertrophied. Single, bipectinate ctenidium. Sexes separate. Epipodial tentacles present surrounding operculum. Radula rhipidoglossate, formula ∼50 + 4 + 1 + 4 + ∼50. Central, lateral teeth strong, solid with smooth cusps. Marginal teeth long, slender, truncate, divided into about 20 toothlets towards distal end.

Remarks

Adult Gigantopelta are easily distinguished from all other described peltospirids by their extremely

COI, cytochrome c oxidase subunit I

large shell size. Furthermore, Gigantopelta can be distinguished from the limpet-like peltospirid genera Ctenopelta Warén & Bouchet, 1993 , Echinopelta McLean, 1989 , Hirtopelta McLean, 1989 , Nodopelta McLean, 1989 , and Rhynchopelta McLean, 1989 , by having a coiled shell with three to four whorls. It can be distinguished from the three skeneiform genera, Pachydermia Warén & Bouchet, 1989 , Depressigyra Warén & Bouchet, 1989 , and Lirapex Warén & Bouchet, 1989 , by its inflated form with a much more depressed spire and larger aperture. The shell surface is nearly smooth, which differs from all peltospirid genera except Depressigyra . The shell roughly resembles that of Peltospira , but has a more tightly coiled initial whorl, and lacks lamellar sculpture. Analysis of the soft parts shows an enlarged oesophageal gland, a feature previously only known from the ‘scaly-foot gastropod’ Chrysomallon squamiferum Chen et al., 2015 ( Warén et al., 2003; Chen et al., 2015), which is also the only other known peltospirid to attain a similar size. In C. squamiferum the oesophageal gland houses symbiotic bacteria, but it is unclear whether this is also the case for Gigantopelta . Gigantopelta can be distinguished from Chrysomallon easily as it does not possess dermal sclerites, has a large operculum, and a shell that is less vertically compressed, with a more circular aperture. The shell of Gigantopelta may be coated in a layer of sulphide, which is frequent amongst vent gastropods including the neomphalins ( Hickman, 1984; Warén & Bouchet, 2001). Gigantopelta is also comparable to the Oligocene fossil genus Elmira Cooke, 1919, from a seep deposit near Bejucal, Cuba whose possible affinity to Neomphalina based on resemblance to Chrysomallon was remarked upon by Kiel & Peckmann (2007). Although the type species Elmira cornuarietis Cooke, 1919, is approximately the same size as Gigantopelta (> 40 mm in shell length), it carries broad revolving grooves, which Gigantopelta lacks. The true taxonomic affinity of Elmira is still unclear.