Benthobrookula galeneae Herbert 2024, sp. nov.

Benthobrookula galeneae sp. nov.

urn:lsid:zoobank.org:act: C64B5682-EAAA-4492-8ADB-3B422EA69100

Figs 24D–F, 25B, G

Diagnosis

Shell elevated-turbiniform, H/D= 1.0–1.11, whorls evenly rounded, base umbilicate; teleoconch sculptured with axial ribs, ± 30 on first whorl, 35–40 on last adult whorl; ribs narrow, not strongly raised, orthocline or slightly opisthocline; intervals between ribs substantially wider than ribs and sculptured by fine, close-set, spiral threads; axial ribs continue to umbilical margin, but evanesce within; umbilicus of moderate width with evenly rounded margin, its interior with indistinct spiral lirae; protoconch globose and exsert.

Etymology

Named after the Galene, the Nereid of calm seas from Greek mythology.

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-2000-38075.

Paratypes

WALTERS SHOAL • 5 empty shells; same collection data as for holotype; MNHN-IM-2000-38076 • 3 empty shells; slopes, stn DW4881; 33°16′ S, 43°50′ E; depth 377–382 m; 2 May 2017; MNHN- IM-2000-38077 • 40 empty shells; slopes, stn DW4886; 33°17′ S, 43°56′ E; depth 573–582 m; 3 May 2017; MNHN-IM-2000-38078 • 6 empty shells; south plain, stn CP4913; 33°52′ S, 44°05′ E; depth 1539–1615 m; 11 May 2017; MNHN-IM-2000-38079.

Description

SHELL. Very small (height up to 1.5 mm), elevated-turbiniform, height ≥ diameter (H/D =1.0–1.11) whorls rounded and suture deeply indented; periphery evenly rounded, close to mid-whorl; base evenly rounded and umbilicate; teleoconch of up to 3.25 whorls. First teleoconch whorl with ± 30 close-set, axial ribs; subsequent whorls with similar ribs, becoming more widely spaced on subsequent whorls, orthocline or slightly opisthocline; last adult whorl usually with 35–40 ribs, but weak or obsolete in some specimens; ribs narrow, but not strongly raised, and thus less blade-like; intervals between ribs substantially wider than ribs; intervals sculptured by close-set microscopic spiral threads (Fig. 25G) and even finer and more close-set axial threads (visible only under SEM); basal sculpture similar; axial ribs continue to umbilical margin, but evanesce within; umbilicus of moderate width and deep, its margin evenly rounded; interior of umbilicus sculptured primarily by indistinct spiral lirae. Aperture subcircular, slightly flattened in parietal region; peristome complete, its edge simple; interior not nacreous.

PROTOCONCH (Fig. 25B). Globose and exsert; diameter ± 220–230 μm, ca 1.25 whorls; with sculpture of fine anastomosing threads producing a network of close-set, irregularly-shaped pits; terminal lip straight, not thickened.

COLOUR. Uniformly translucent milky-white when fresh.

DIMENSIONS. Holotype, height 1.35 mm, diameter 1.23 mm; largest specimen, height 1.50 mm, diameter 1.3 mm.

Distribution

Known only from the slopes and surrounding plain of Walters Shoal, at depths of 382–1539 m; on sandy substrata with cnidarians, crustaceans and echinoderms; living specimens unknown.

Remarks

In comparison with the other species of Benthobrookula from Walters Shoal, this material has more numerous, more close-set axial ribs, ca 30 on the first whorl and 35–40 on the last adult whorl. However, there is considerable variation in the strength of the ribs on the last adult whorl, some specimens appearing to have only spiral lirae at this stage. Such specimens may thus resemble Be. semisculpta sp. nov., but that species has a deeper final whorl, a less prominent spire and the axial ribs on the spire are prosocline and distinctly curved, rather than orthocline.

Benthobrookula pfefferi (Powell, 1951) from South Georgia is perhaps the most similar species, but that species has a larger protoconch (diameter 330–400 vs 220–230 μm) and a narrower umbilicus with stronger peri-umbilical spiral sculpture (Zelaya et al. 2006). Benthobrookula gemmula (Turton, 1932), a rather variable but poorly known species widespread off the east coast of South Africa (Kilburn 1977; Herbert 2015), has similar sculpture, but the original photograph provided by Turton shows a shell with a much more prominent spire.