Benthobrookula scalaroides, 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 : 60-61

Benthobrookula scalaroides sp. nov.

urn:lsid:zoobank.org:act:8261B816-4DC9-4D46-A58F-D4F056DE1951

Figs 24J–L , 25D, I

Diagnosis

Shell elevated-turbiniform, H/D =1.1–1.2, whorls evenly rounded, suture deeply indented, base umbilicate; teleoconch sculptured with widely-spaced, sharp, orthocline, axial ribs; first whorl with ± 17 ribs, penultimate whorl with ± 20 ribs; ribs sometimes more close-set in last quarter whorl; rib intervals with microscopic spiral threads; basal sculpture similar, ribs continuing into umbilicus; peristome complete; protoconch globose and exsert.

Etymology

From the Latin “ scala ” – “a flight of stairs”; in reference to the strongly ribbed sculpture.

Material examined

Holotype

WALTERS SHOAL • empty shell; slopes, stn DW4886; 33°17′ S, 43°56′ E; depth 573–582 m; 3 May 2017; MNHN-IM-2000-38084 .

Paratypes

WALTERS SHOAL – slopes • 16 empty shells; same collection data as for holotype; MNHN- IM-2000-38085 • 3 empty shells; stn DW4887; 33°17′ S, 43°57′ E; depth 599–640 m; 3 May 2017; MNHN-IM-2000-38086 • 1 empty shell; stn DW4899; 33°09′ S, 44°02′ E; depth 707–720 m; 6 May 2017; MNHN-IM-2000-38087 .

Description

SHELL. Very small (height up to 1.3 mm), elevated-turbiniform; higher than wide (H/D = 1.1–1.2); whorls strongly rounded and suture deeply indented; periphery evenly rounded, close to mid-whorl; base rounded, deeply umbilicate; teleoconch of up to 3.25 whorls. First teleoconch whorl with ± 17 axial ribs, increasing in strength toward end of whorl; subsequent whorls with similar ribs, orthocline and progressively more widely spaced until final quarter of last adult whorl where they usually (but not always) become more close-set; penultimate whorl with ± 20 ribs; ribs narrow and blade-like, sometimes appearing weakly alate below adapical suture; intervals between ribs substantially wider than ribs, particularly on final two whorls; intervals sculptured by close-set, microscopic spiral threads ( Fig. 25I ) and even finer and more close-set axial threads (visible only under SEM); basal sculpture similar, continuing into umbilicus; umbilicus relatively narrow and deep, its margin evenly rounded. Aperture circular; peristome complete, its edge simple; interior not nacreous.

PROTOCONCH ( Fig. 25D ). Globose and exsert; diameter 200–210 μm, ca 1.25 whorls; where unworn sculptured by fine anastomosing threads producing a network of close-set, irregularly-shaped pits; terminal lip more or less straight, not thickened.

COLOUR. Uniformly white; freshest specimens somewhat translucent.

DIMENSIONS. Holotype, height 1.14 mm, diameter 0.98 mm; largest specimen, height 1.3 mm.

Distribution

Known only from the slopes of Walters Shoal, at depths of 582–707 m; dredged on substrata of coarse sand; living specimens unknown.

Remarks

Other somewhat elevated species of Benthobrookula include Be. charleenae (Schwabe & Engl, 2008) , Be. kerguelensis ( Thiele, 1925), Be. nepeanensis (Gatliff, 1906) and Be. strebeli (Powell, 1951). Benthobrookula charleenae , from over 2900 m off the South Sandwich Islands, differs in having more close-set axial ribs (27 vs 20 on penultimate whorl) and a larger protoconch (diameter 280 vs 200– 210 μm). In Be. kerguelensis the shell is larger (height 1.6 mm) and, judging from the original figure, the last adult whorl is deeper and the spire less elevated. Benthobrookula nepeanensis from southern Australia has an even more elevated spire and a much narrower umbilicus, whereas in Be. strebeli from South Georgia the axial ribs are more prosocline and less blade-like, and the base is imperforate with more conspicuous spiral sculpture (holotype figured by Zelaya et al. 2006: fig. 6a).

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.