Benthobrookula araneum Herbert 2024, sp. nov.
Creators: name: Herbert, David G.
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Gastropoda
Seguenziida
Unassigned
Benthobrookula
Benthobrookula araneum

description: Benthobrookula araneum sp. nov.
urn:lsid:zoobank.org:act: 51E19EE6-CE0C-4554-BE8A-10311EAE3267
Figs 24A–C, 25A, F
Diagnosis
Shell turbiniform, H/D=0.83–1.0, whorls evenly rounded, broadly umbilicate; teleoconch sculptured with axial ribs, 23–24 on first whorl, 20–23 ribs on last adult whorl, never crowded behind outer lip; ribs prosocline, their intervals substantially wider than ribs and sculptured by fine, close-set, spiral threads; ribs less elevated with more rounded crests on base, continuing into umbilicus in some specimens; umbilical margin evenly rounded, its interior with indistinct spiral lirae; protoconch globose and exsert.
Etymology
From the Latin “ araneum ” – “a cobweb” (noun in apposition); in reference to the web-like interaction of axial cords and spiral threads.
Material examined
Holotype
WALTERS SHOAL • empty shell; slopes, stn DW4887; 33°17′ S, 43°57′ E; depth 599–640 m; 3 May 2017; MNHN-IM-2000-38068.
Paratypes
WALTERS SHOAL – slopes • 7 empty shells; same collection data as for holotype; MNHN- IM-2000-38069 • 1 empty shell; stn DW4898; 33°09′ S, 44°01′ E; depth 652–668 m; 6 May 2017; MNHN-IM-2000-38070 • 8 empty shells; stn DW4899; 33°09′ S, 44°02′ E; depth 707–720 m; 6 May 2017; MNHN-IM-2000-38071 • 2 empty shells; stn DW4900; 33°10′ S, 44°01′ E; depth 660–670 m; 6 May 2017; MNHN-IM-2000-38072 • 1 empty shell; stn CP4902; 33°08′ S, 44°02′ E; depth 700– 711 m; 7 May 2017; MNHN-IM-2000-38073 • 2 empty shells; stn CP4906; 33°26′ S, 44°00′ E; depth 799–837 m; 9 May 2017; MNHN-IM-2000-38074.
Other material
WALTERS SHOAL – slopes • 4 empty shells; stn DW4886; 33°17′ S, 43°56′ E; depth 573–582 m; 3 May 2017; MNHN • 2 empty shells; stn CP4907; 33°27′ S, 44°00′ E; depth 880 m; 9 May 2017; MNHN.
Description
SHELL. Very small (height up to 1.23 mm), turbiniform; diameter ≥ height (H/D =0.83–1.0); whorls rounded and suture distinctly indented; periphery evenly rounded, close to mid-whorl; base rounded, broadly umbilicate; teleoconch of 2.75–3.0 whorls. First teleoconch whorl with 23–24 axial ribs of similar strength, first one short, not extending to abapical suture; ribs more elevated and more prosocline on subsequent whorls, but not increasing in number, narrow and blade-like, their intervals progressively wider; 20–23 ribs on last adult whorl, persisting to end of whorl in most specimens (though last few rather indistinct), but cease up to one quarter-whorl behind outer lip in others; never crowded behind outer lip; intervals between ribs substantially wider than ribs, particularly on final two whorls; intervals sculptured by fine, close-set, spiral threads (Fig. 25F), and even finer and more close-set axial threads (visible only under SEM); ribs continue on to base, but become less elevated, their crests rounded or even flattened, rather than sharp; ribs continue into umbilicus in some specimens, but evanesce at its margin in others; umbilicus relatively wide, margin evenly rounded; interior of umbilicus variably sculptured with fine, rather indistinct spiral lirae. Aperture circular; peristome complete, its edge simple; interior not nacreous.
PROTOCONCH (Fig. 25A). Globose and exsert; diameter ±220 μm, ca 1.25 whorls; sculptured with fine, anastomosing threads creating an irregular pattern of microscopic pits; terminal lip straight or weakly convex, not thickened.
COLOUR. Uniformly white; freshest specimens somewhat translucent.
DIMENSIONS. Holotype, height 1.23 mm, diameter 1.38 mm (= largest specimen).
Distribution
Known only from the slopes of Walters Shoal, at depths of 582–880 m; on coarse sandy substrata with abundant crustaceans, echinoderms and solitary corals; living specimens unknown.
Remarks
Benthobrookula aethiopica (Thiele, 1925) from 1134 m off Somalia, is of similar size and proportions (H/D ±1.0), but has 28 axial ribs on the last adult whorl and reportedly lacks spiral sculpture. Benthobrookula valdiviae (Thiele, 1925) from a depth of 693 m off the Kenya-Somalia border and Be. kerguelensis (Thiele, 1925) from an unspecified depth in the Southern Ocean, both have a similar number of axial ribs to Be. araneum sp. nov., but both are proportionately taller (H/D ± 1.17–1.19), have a narrower umbilicus and reach a larger size (height 2.1 mm and 1.6 mm respectively). In Be. kerguelensis, the holotype of which was recently figured by Engl (2012: pl. 25 fig. 1), the axial ribs are more robust than in Be. araneum.
Benthobrookula pfefferi (Powell, 1951) from South Georgia is also somewhat similar, but it has a more elevated shell with more numerous axial ribs (36–38 on last adult whorl), and attains a larger size (height 1.83 mm) (Zelaya et al. 2006). In terms of overall shell shape and proportions, and the number of axial ribs, perhaps the most similar species is Be. conica (Watson, 1886) from off Brazil (Absalão et al. 2001), but that species has more robust axial ribs which remain strong in the umbilicus and the umbilical margin lacks spiral cords.
description: Published as part of Herbert, David G., 2024, The Vetigastropoda (Mollusca) of Walters Shoal, with descriptions of two new genera and thirty new species, pp. 1-119 in European Journal of Taxonomy 923 on pages 54-57, DOI: 10.5852/ejt.2024.923.2445, http://zenodo.org/record/10727741