Trenchia mcleani sp. nov.

urn:lsid:zoobank.org:act: 15A3EF83-0D84-40E8-A2E3-69A4CA507FE3

Fig. 26D–F, H

Diagnosis

Shell small, wider than high, whorls rapidly expanding; spire flattened; spire whorls with low but distinct spiral rib at whorl summit, evanescing on second half of last adult whorl; base with a strong carina emerging from point of insertion of columella lip; a stronger, flange-like carina bordering and spiralling into umbilicus; aperture large, distinctly flattened in columella region; columella lip almost vertical; umbilicus wide. Protoconch evidently lacking spiral sculpture.

Etymology

Named for the late Dr James H. McLean (Natural History Museum, Los Angeles County), in recognition of his very considerable contribution to vetigastropod taxonomy and systematics, and of his friendship and support during my early career.

Material examined

Holotype

WALTERS SHOAL • empty shell; south plain, stn CP4913; 33°52′ S, 44°05′ E; depth 1539–1615 m; 11 May 2017; MNHN-IM-2000-38093.

Paratypes

WALTERS SHOAL • 3 empty shells; same collection data as for holotype; MNHN-IM-2000-38094.

Description

SHELL. Small (diameter up to 2.9 mm), wider than high (H/D ± 0.69); teleoconch of up to 2.25 rapidly expanding whorls; spire flattened and slightly tilted, scarcely protruding above penultimate whorl; spire whorls with low but distinct spiral rib at whorl summit, prior to descent toward indented adapical suture; angulation begins as rounded ridge immediately after terminal lip of protoconch, subsequently weakening and evanescing on second half of last adult whorl; periphery evenly rounded; base with strong carina emerging from point of insertion of columella; a similar but stronger, flange-like carina marks border of umbilicus, ending at junction of basal and columella lips and spiralling steeply into umbilicus; inner portion of base between keels more or less flat, but flaring out to form umbilical keel; sculpture of close-set, microscopic, collabral threads and stronger, uneven growth-lines; no spiral microsculpture evident. Aperture weakly prosocline, roundly D-shaped, columella region distinctly flattened; peristome complete; inner lip mostly straight and almost vertical (slightly angled toward base of shell axis); thickened and flaring where umbilical keel meets basal lip; parietal lip short; outer lip and interior smooth.

PROTOCONCH (Fig. 26H). Diameter ± 275 μm, comprising ca 1.25 whorls; apical bulb rounded, but not globose or exsert; suture between apical bulb and terminal tube distinct; surface somewhat eroded but seemingly smooth, no spiral sculpture evident; terminal lip convex, not thickened.

COLOUR. Uniformly cream-white, opaque.

DIMENSIONS. Holotype, height 2.0 mm, diameter 2.9 mm (= largest specimen).

Distribution

Known only from the plain surrounding Walters Shoal, at depths of 1539–1615 m; trawled on coarse sandy substrata; living specimens unknown.

Remarks

Trenchia mcleani sp. nov. has a lower spire and more rapidly expanding last adult whorl than any other species of Trenchia. The most geographically proximate species, T. agulhasae (Clarke, 1961), from abyssal depths in the Cape Basin, 1600 km SW of Cape Town, has a much more prominent spire and less auriform shape (holotype illustrated by McLean 1992: fig. 58). Perhaps the most similar species is T. biangulata Rubio & Rolán, 2013 from the NE Atlantic, which also has a relatively low spire and strong peri-umbilical carina, but that species has a stronger shoulder carina, narrower umbilicus and a shorter, more oblique columella lip, as well as a less auriform shape (Hoffman et al. 2020).