The Vetigastropoda (Mollusca) of Walters Shoal, with descriptions of two new genera and thirty new species Author Herbert, David G. text European Journal of Taxonomy 2024 2024-02-28 923 1 119 https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2445/10835 journal article 10.5852/ejt.2024.923.2445 2118-9773 10727741 AD68CEDD-2F2D-4010-BE7A-1B1AE9E4A0F3 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).