Bathymophila williamsae, Herbert, 2024

Herbert, David G., 2024, The Vetigastropoda (Mollusca) of Walters Shoal, with descriptions of two new genera and thirty new species, European Journal of Taxonomy 923, pp. 1-119 : 86-89

Bathymophila williamsae sp. nov.

urn:lsid:zoobank.org:act:8EA9EED9-2F46-4B59-BA24-3D8F24B511CC

Figs 35A–D , 36D–E

Diagnosis

Shell conispiral, wider than high, diameter up to 8.8 mm; spire prominent with shouldered whorls; periphery rounded, below mid-whorl; shell smooth except for coronations at shoulder angulation and spiral lirae on apical whorls; columella reflected and much thickened by deposition of callus, occluding umbilicus; callus lustreless and microscopically granular, lacking discrete swellings or bosses; shell greyish-white with translucent collabral bands.

Etymology

Named for Dr Suzanne T. Williams of the Natural History Museum, London, in recognition of her insightful contributions concerning vetigastropod systematics.

Material examined

Holotype

WALTERS SHOAL • living specimen; slopes, stn CP4918; 32°58′ S, 43°27′ E; depth 1295–1356 m; 14 May 2017; DNA tissue sample; MNHN-IM-2013-67177 .

Paratypes

WALTERS SHOAL • 1 living specimen; south plain, stn CP4913; 33°52′ S, 44°05′ E; depth 1539–1615 m; 11 May 2017; DNA tissue sample; MNHN-IM-2013-67175 • 1 living specimen; same collection data as for preceding; DNA tissue sample; MNHN-IM-2013-6717 • 1 living specimen; slopes, stn CP4918; 32°58′ S, 43°27′ E; depth 1295–1356 m; 14 May 2017; DNA tissue sample; MNHN-IM-2013-67178 • 10 empty shells; slopes, stn CP4920; 32°52′ S, 43°31′ E; depth 1210–1293 m; 14 May 2017; MNHN- IM-2000-35715 .

Other material

WALTERS SHOAL • 9 empty shells, juvenile; south plain, stn CP4913; 33°52′ S, 44°05′ E; depth 1539–1615 m; 11 May 2017; MNHN • 1 empty shell; slopes, stn CP4917; 32°55′ S, 43°27′ E; depth 1296–1375 m; 13 May 2017; MNHN .

Description

SHELL. Of moderate size for genus (diameter up to 8.8 mm), conispiral, wider than high (H/D =0.81– 0.85); spire prominent, its whorls convex, but not strongly so, suture relatively shallowly indented; spire whorls shouldered, last adult whorl not so; periphery rounded, below mid-whorl; sculpture weak, shell essentially smooth and glossy save for coronations at shoulder angulation and spiral lirae on apical whorls; base weakly convex, umbilicus occluded by callus deposit; teleoconch of up to 4.75 whorls. First two teleoconch whorls with 6–7 relatively strong spiral lirae with close-set, microscopic axial pliculae in their intervals ( Fig. 36D ); uppermost lira delimiting distinct shoulder; spiral lirae weaken and become obsolete during third whorl (sometimes quite abruptly so), the shell becoming smooth and glossy; shoulder angle remains, usually developing into raised subsutural cord with numerous low coronations; strength of cord and its coronations somewhat variable between specimens, very weak in some; cord wanes with growth and coronations usually absent on last adult whorl; the latter with only indistinct growth-lines that extend onto base, strengthening somewhat near umbilical callus; base otherwise smooth save for traces of indistinct spiral lirae; umbilicus lacking, occluded by columella callus even in subadults. Aperture subquadrate to roundly D-shaped; peristome interrupted in parietal region; columella concave, reflected and much thickened by deposition of callus so as to occlude umbilicus; callus lustreless and microscopically granular, lacking discrete swellings or bosses; outer lip thin and simple; interior nacreous, lacking labral ornamentation.

PROTOCONCH ( Fig. 36E ). Whitish, somewhat translucent; diameter ± 400 μm, ca 1.25 whorls, apical beak lacking; surface texture finely granular with traces of widely spaced spiral threads; terminal lip straight, not thickened.

COLOUR. Greyish-white with translucent collabral bands when fresh, traces of pink/green iridescence evident; older, post-mortem specimens more opaque.

DIMENSIONS. Holotype, height 6.9 mm, diameter 8.5 mm; largest specimen, height 7.5 mm, diameter 8.8 mm.

OPERCULUM. Corneous, pale straw-brown, multispiral with short growing edge.

RADULA AND EXTERNAL ANATOMY. Unknown.

Distribution

Known only from the slopes and surrounding plain of Walters Shoal, at depths of 1293–1539 m (live-taken material 1356–1539 m); obtained by beam trawl on fine sand with diverse echinoderms, cnidarians and crustaceans.

Remarks

The umbilicus is consistently occluded by callus in all adult and subadult specimens. A single juvenile of 3.5 teleoconch whorls retains a patent umbilicus, but this is already narrowed and partially occluded by the progressively thickened columella base.

When compared with other Indo-West Pacific species of Bathymophila , B. williamsae sp. nov. is unusual in lacking one or more swellings or bosses on the basal portion of the columella callus. Most also have more flat-sided whorls. Some specimens of B. gravida Marshall, 1999 , from off northern New Zealand, also have convex whorls, but that species attains a larger size (diameter up to 16 mm) and has nodular spiral cords around the umbilicus. The only other species of Bathymophila recorded from the south-western Indian Ocean, B. stephanephoros Vilvens, 2022 from the northern Mozambique Channel, is somewhat smaller (diameter <6.3 mm), has a strongly coronated subsutural cord and bears two nodules on the umbilical callus. Preliminary analysis of CO1 sequence data indicates that samples of B. williamsae cluster as a well-defined monophyletic clade amongst other Bathymophila species (S.T. Williams pers. com. 2021).

Figures

Fig. 35. A–D. Bathymophila williamsae sp. nov., holotype, diameter 8.5 mm (MNHN-IM-2013-67177). E–H. Phragmomphalina vilvensi Herbert & Williams, 2020. E–G. Walters Shoal, stn CP4907, diameter 14.7 mm (MNHN-IM-2013-67173). H. Large specimen with weak subsutural sculpture, Walters Shoal, stn CP4907, diameter 15.3 mm (MNHN). I–L. Phragmomphalina candida sp. nov. I–K. Holotype, diameter 12.8 mm (MNHN-IM-2000-35716). L. Subadult lacking umbilical septum, diameter 9.0 mm (paratype, MNHN-IM-2000-35718).

Fig. 36. A–C, H–I. Solariella asaphea sp. nov. A, C. Apertural and oblique basal views of holotype, diameter 4.1 mm (MNHN-IM-2000-35719). B. Apical view of paratype, diameter 3.3 mm (MNHN- IM-2000-35720). H. Subsutural sculpture, holotype. I. Protoconch (paratype, MNHN-IM-2000-35720). D–E. Bathymophila williamsae sp. nov., paratype (MNHN-IM-2013-67176). D. Oblique view of spire showing detail of apical sculpture. E. Sculptural detail of protoconch. F–G. Phragmomphalina candida sp. nov., paratype (MNHN-IM-2000-35718). F. Oblique view of spire showing sunken suture and detail of apical sculpture. G. Sculptural detail of protoconch. Scale bars: D, F =500 μm; E, G, I= 100 μm; H =200 μm.