Gigantopelta chessoia Chen & Linse & Roterman & Copley & Rogers 2015, SP. NOV.
Creators: name: Chen, Chong
name: Linse, Katrin
name: Roterman, Christopher N.
name: Copley, Jonathan T.
name: Rogers, Alex D.
Publisher: name: Zenodo
Year: 2015
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Gastropoda
Neomphalida
Peltospiridae
Gigantopelta
Gigantopelta chessoia

description: GIGANTOPELTA CHESSOIA SP. NOV. (FIGS 2–7)
‘Peltospiroidea n. sp. ’ – Rogers et al., 2012: 7, fig. 3d. ‘Undescribed species of peltospiroid gastropod’ – Marsh et al., 2012: 6, fig. 5c, j.
Type material
Holotype. Shell diameter 36.30 mm, 99% ethanol, Figure 3A–C. E 2 segment, East Scotia Ridge, 56°05.31′S, 30°19.10′W (‘Cindy’s Castle’), 2606 m deep, RRS James Cook expedition JC42, ROV Isis Dive 130, 20.i.2010, leg. A. D. Rogers (NHMUK 20150066). Paratypes. One dissected specimen, 99% ethanol (shell diameter 31.12 mm, Fig. 4A, B; NHMUK 20150067); growth series of five specimens, 99% ethanol (NHMUK 20150068). The above two lots have same collection data as the holotype. Growth series of five specimens, 99% ethanol (OUMNH. ZC.2013.02.002); two specimens, 99% ethanol (CAMZM 2015.2.1 -2); growth series of five specimens, 99% ethanol (SMNH Type Collection 8450); five specimens, 10% buffered formalin (NHMUK 20150069). Collection data for the latter three lots: E2 segment, East Scotia Ridge, 56°05.34′S, 30°19.07′W (‘ Cindy’s Castle’), depth 2644 m, RRS James Cook expedition JC42, ROV Isis Dive 134, 24.i.2010, leg. A. D. Rogers.
Other material examined
Approximately 200 specimens collected on RRS James Cook expedition JC42 with ROV Isis, on dives 130, 134, and 141. Collection data for dive 130: same as holotype; dive 134: same as listed for paratype series; dive 141: E9 segment, East Scotia Ridge, 60°02.81′S, 29°58.71′W (‘Marsh Tower’), depth 2394 m, RRS James Cook expedition JC42, ROV Isis Dive 141, 30.i.2010, leg. A. D. Rogers.
Etymology
The species is named after the ChEsSo (Chemosynthetically-driven ecosystems south of the Polar Front: biogeography and ecology) Consortium (Natural Environment Research Council (NERC) Grant NE/DO 1249X/1), which led to the discovery of ESR hydrothermal vents and this species.
Zoobank registration urn:lsid:zoobank.org:act: D46EB848-506D-45B7-8D05- 35535592BD1E
Description/Diagnosis
Shell: Shell (Fig. 4A, B) globose, three to four whorls, coiled tightly with a deep suture. Spire depressed. Aperture roughly circular, very large. Ratio of shell diameter to aperture length approximately 1:0.633 (average of 100 specimens). Shell trochiform to neritiform, holostomous. Protoconch (Fig. 5A) consists of 0.5 whorls, diameter about 210 μm. Irregular reticulate ornament present initially, becoming obsolete distally. Suture around protoconch very deep. Teleoconch smooth, no distinct sculpture. Subtle growth lines, irregular protuberances present. Growth lines stronger on the body whorl, especially near the aperture. Periostracum thick, dark olive, enveloping the aperture. Ostracum and hypostracum milky white. Thin, fragile without periostracum. Columellar folds lacking. Callus extends to slightly cover columellar. Area around callous concave. Maximum shell diameter 45.7 mm.
Operculum: Operculum (Fig. 3C) with central nucleus, multispiral, thin, flaky on fringe. Operculum fringe often damaged. Juveniles operculum thin, semitransparent, fringe not flaky (Fig. 5C).
Radula: Radula (Fig. 6A) rhipidoglossate. Ribbon approximately 0.5 mm wide and 4 mm long in adults. Formula ∼50 + 4 + 1 + 4 + ∼50. Central, lateral teeth cusp-like, pointed (Fig. 6C). Marginal teeth long, slender, bearing ∼20 denticles at distal end (Fig. 6E). Central tooth triangular, very broad at base, tapering dis- tally, smooth, no sculpture. Lateral teeth solid, bearing a clear protrusion at base.
Soft parts (Fig. 7A): Foot muscular, large. Fully retractable into shell, red when alive. Small epipodial tentacles present, surrounding posterior two-thirds of operculum. Cephalic tentacles thick, triangular, broad at base and thinning towards tips. Eyes lacking. Snout tapering, thick. Oesophageal gland huge, approximately same size as aperture. Ctenidium bipectinate. Sexes separate. Shell muscle large, horse-shoe shaped. Intestine forms a simple loop.
Distribution
Only known from hydrothermal vents on segment E2 (56°05.2′S to 56°05.4S, 30°19.00′W to 30°19.35′W) and E9 (60°02.50′S to 60°03.00′S, 29°58.60′W to 29°59.00′W) of ESR. This species forms dense aggregations rather close to vent effluents.
Remarks
The dispersal mechanism is inferred to be nonplanktotrophic from the protoconch, presumably with a planktonic dispersal stage. Table 2 shows the shell parameters of G. chessoia. The relationships between the six shell parameters measured were investigated and they were all linear across all life stages. Figure 8 shows a scatter plot of shell diameter against shell height. See Rogers et al. (2012) for details on location of hydrothermal vent sites.
Comparative remarks
Similar to Gigantopelta aegis sp. nov. described below. Gigantopelta chessoia can be distinguished as it has a taller spire, less extensive callus, and area around callus is concave and not flattened as in G. aegis. Differences are seen in the structure of the radula. The central tooth of G. chessoia is much wider at the base and triangular compared with that of G. aegis, which is rectangular. Lateral teeth are sculptured in both species, but the marks occur nearer to the base of the teeth in G. aegis. Gigantopelta chessoia can also be easily distinguished by the lack of sulphide deposits on the shell and operculum, at least from G. aegis found in Longqi Field, the only known habitat to date. Similarly, the operculum in G. aegis is much thicker than G. chessoia at all life stages.
description: Published as part of 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), pp. 319-335 in Zoological Journal of the Linnean Society (Zool. J. Linn. Soc.) (Zool. J. Linn. Soc.) 175 (2) on pages 323-327, DOI: 10.1111/zoj.12279, http://zenodo.org/record/5338416