Benthobrookula semisculpta, 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 : 61-62

Benthobrookula semisculpta sp. nov.

urn:lsid:zoobank.org:act:4FA6CCE8-FA2E-4B11-BCAF-F37EDC68D677

Figs 24M–O , 25E

Diagnosis

Shell relatively thick, turbiniform, H/D=0.81–0.93, whorls strongly rounded and suture deeply indented, base umbilicate; first two teleoconch whorls with 24–27 curved axial ribs, their intervals with fine, close-set, spiral threads; sculpture evanescing during first half of third whorl, but traces of spiral threads may remain; base smooth, with only traces of microscopic growth-lines; umbilicus relatively wide with rounded margin, its interior with indistinct spiral lirae; peristome complete; protoconch globose and exsert.

Etymology

From the Latin “ semis ” – “half” and “ sculptus ” – “carved”; in reference to the sculptured spire whorls and smooth final whorl.

Material examined

Holotype

WALTERS SHOAL • empty shell; slopes, stn CP4906; 33°26′ S, 44°00′ E; depth 799–837 m; 9 May 2017; MNHN-IM-2000-38088 .

Paratypes

WALTERS SHOAL – slopes • 1 empty shell; stn DW4898; 33°09′ S, 44°01′ E; depth 652–668 m; 6 May 2017; MNHN-IM-2000-38089 • 4 empty shells; stn CP4911; 32°46′ S, 44°18′ E; depth 964–965 m; 10 May 2017; MNHN-IM-2000-38090 .

Description

SHELL. Very small (height up to 1.35 mm), relatively thick, turbiniform; wider than high (H/D =0.81– 0.93); spire whorls strongly rounded and suture deeply indented; periphery evenly rounded, close to mid-whorl; base rounded and umbilicate; teleoconch of up to 2.75–3.0 whorls. First two teleoconch whorls with 24–27 curved axial ribs, progressively more widely spaced; ribs evanescing during first half of third whorl; intervals between ribs with fine, relatively close-set spiral threads on first two teleoconch whorls; threads buttressing ribs but seeming not to cross rib crests ( Fig. 25E ); additional weaker axial threads cross spiral threads in rib intervals, most noticeable toward whorl periphery (visible only under SEM); this microsculpture also evanescing on third whorl, but traces of spiral threads may remain; base evenly rounded, smooth, with only traces of microscopic growth-lines; umbilicus relatively wide, its margin rounded; interior of umbilicus with fine, indistinct spiral lirae and traces of axial ribs of spire whorls deep within. Aperture circular; peristome complete, its edge simple; upper part of outer lip gently convex; interior not nacreous.

PROTOCONCH ( Fig. 25E ). Globose and exsert; diameter ± 220 μm, ca 1.25 whorls; with fine anastomosing sculpture creating network of minute, irregularly-shaped pits; terminal lip prosocline, weakly convex, not thickened.

COLOUR. Uniformly white, somewhat glossy.

DIMENSIONS. Holotype, height 1.35 mm, diameter 1.45 mm (= largest specimen).

Distribution

Known only from the slopes of Walters Shoal, at depths of 668–964 m; dredged on coarse sandy substrata; living specimens unknown.

Remarks

I have chosen to refer this species to Benthobrookula on account of the coarse ribs and fine spiral threads on the spire whorls. However, within this genus Be. semisculpta sp. nov. is rendered distinctive on account of its evanescing sculpture on the latter half of the last adult whorl and the collabral curvature of the axial ribs on the spire whorls. Although some individuals of other species show reduced or obsolete axial sculpture prior to the outer lip, it is not as extensive as in the present species and the spiral sculpture remains distinct.

Figures

Fig. 24. A–C. Benthobrookula araneum sp. nov. A–B. Holotype, height 1.2 mm (MNHN-IM-2000- 38068). C. Paratype, diameter 1.1 mm (MNHN-IM-2000-38069). D–F. Benthobrookula galeneae sp. nov. D–E. Holotype, height 1.25 mm (MNHN-IM-2000-38075). F. Paratype, diameter 1.2 mm (MNHN-IM-2000-38076). G–I. Benthobrookula laticostata sp. nov. G–H. Holotype, diameter 1.0 mm (MNHN-IM-2000-38080).I.Paratype,diameter1.0mm(MNHN-IM-2000-38082).J–L.Benthobrookula scalaroides sp. nov. J–K. Holotype, height 1.14 mm (MNHN-IM-2000-38084). L. Paratype, diameter 1.0 mm (MNHN-IM-2000-38085). M–O. Benthobrookula semisculpta sp. nov. M–N. Holotype, height 1.4 mm (MNHN-IM-2000-38088). O. Paratype, diameter 1.4 mm (MNHN-IM-2000-38090).

Fig. 25. A, F. Benthobrookula araneum sp. nov. A. Protoconch (paratype, MNHN-IM-2000-38069). F. Sculptural detail at start of last adult whorl, holotype. B, G. Benthobrookula galeneae sp. nov. B. Protoconch (paratype, MNHN-IM-2000-38076). G. Sculptural detail at start of last adult whorl, holotype. C, H. Benthobrookula laticostata sp. nov. C. Protoconch, DW4899 (paratype, MNHN- IM-2000-38082. H. Sculptural detail at start of last adult whorl, holotype. D, I. Benthobrookula scalaroides sp. nov. D. Protoconch (paratype, MNHN-IM-2000-38085). I. Sculptural detail at start of last adult whorl, holotype. E. Benthobrookula semisculpta sp. nov., protoconch CP4911 (paratype, MNHN-IM-2000-38090). Scale bars=100 μm.