Gigantopelta aegis 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 aegis

description: GIGANTOPELTA AEGIS SP. NOV. (FIGS 2–7)
Type material
Holotype. Shell diameter 37.61 mm, 99% ethanol, Figure 3D–F. Longqi vent field, Southwest Indian Ridge, 37°47.03′S, 49°38.97′E (‘Tiamat’), 2785 m deep, RRS James Cook expedition JC67, ROV Kiel 6000 Dive 142, 29.xi.2011, leg. J. T. Copley (NHMUK 20150070). Paratypes. One dissected specimen, 99% ethanol (shell diameter 35.24 mm, Fig. 4C, D; NHMUK 20150071); growth series of five specimens, 99% ethanol (NHMUK 20150072); growth series of five specimens, 99% ethanol OUMNH. ZC. 2013.02.003); two specimens, 99% ethanol (CAMZM 2015.3.1 -2); growth series of five specimens (SMNH Type Collection 8451). All paratypes above have the same collection data as holotype. Five specimens, 10% buffered formalin (NHMUK 20150073): Longqi vent field, Southwest Indian Ridge, 37°47.03′S, 49°38.96′E (‘Tiamat’ chimney), 2783 m deep, RRS James Cook expedition JC67, ROV Kiel 6000 Dive 140, 27.xi.2011, leg. J. T. Copley (NHMUK 20150073).
Other material examined
Approximately 200 specimens, same collection data as the holotype.
Etymology
Aegis (Latin), the shield of Zeus and Athena. The specific name is an allusion of the thick and large sulphidecovered operculum to the mythical shield.
Zoobank registration urn:lsid:zoobank.org:act: 45E3E373-E126-4179-B1EB- D583FCFB3D12)
Description/Diagnosis
Shell: Shell (Fig. 4B) globose, three to four whorls, trochiform to neritiform. Spire depressed. Aperture holostomous. Tightly coiled. Suture deep. Aperture very large, circular, body whorl to aperture length ratio approximately 1:0.65 (average of 100 specimens). Protoconch (Fig. 5B) 0.5 whorls, about 210 μm in length, sculpture unknown (surface layer of examined specimens affect- ed by dissolution). Thick, orange to reddish sulphide layer covers periostracum. Periostracum dark olive with sulphides removed. Ostracum milky white. Ostracum thin, fragile without sulphide and periostracum. Periostracum slightly recurved at aperture. Columellar folds lacking. Callus extends extensively, covering columellar region. Area around callus flattened (dark area in Fig. 3F). Shell smooth, lacking sculpture. Fine growth lines, subtle spiral cords present under sulphide layer. Maximum shell diameter 44.2 mm.
Operculum: Operculum (Fig. 3E, F) corneous, thin, flaky near the fringe, multispiral, covered by thick sulphide layer except outermost whorl, same material as those covering shell. Juvenile operculum lacking sulphide layer. Moderately thick, opaque, with concave shape (Fig. 5B).
Radula: Radula (Fig. 6B) rhipidoglossate. Ribbon in adults approximately 0.5 mm wide and 4 mm long. Formula ∼50 + 4 + 1 + 4 + ∼50. Central, lateral teeth (Fig. 6D) with sharp cusps. Central tooth rectangular. Lateral teeth bear a protrusion near the base. Marginal teeth (Fig. 6F) elongate with truncate distal ending, dividing into ∼20 denticles.
Soft parts (Fig. 7B): Foot muscular, large. Fully retractable. Pale white when alive. Small epipodial tentacles present, surrounding posterior two-thirds of operculum. Cephalic tentacles thick, broad at base, tapering distally. Snout tapering and thick. Oesophageal gland huge (see Fig. 7B). Intestines forming a simple loop. Ctenidium bipectinate. Sexes separate. Gonads rather displaced towards the head-foot. Shell muscle large, horse-shoe shaped.
Distribution: Only known from Longqi vent field, SWIR (approximately 37°47.03′S, 49°38.96′E), around 2700 m depth. Found mostly on areas of diffuse flow but also on chimneys of active black smokers.
Remarks
Similar to Gigantopelta chessoia sp. nov.; see Comparative remarks above for comparison. The sulphide covering of the shell and that forming the thick coating on the operculum is remarkable. The coating only covers the outer side, and can be removed from the operculum intact by inserting a blade in between. The adult shells are completely covered with sulphide. Sulphide deposition appears to start very early in development, and from the protoconch; as in young specimens (∼ 5 mm maximum diameter) sulphide is only present as a tablet on the apex and not covering the whole shell. The shell parameters are given in Table 2. The relationships between the six parameters measured were investigated, and they were linear across all life stages. Figure 8B shows a scatter plot of shell diameter against shell height.
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 327-329, DOI: 10.1111/zoj.12279, http://zenodo.org/record/5338416