Ilanga discus Herbert, 1987

(Figs 5 A–L, Key 1: 1)

DNA ref: Ilanga discus (Williams et al. 2013; Sumner-Rooney et al. 2016)

COI sequence data: GenBank Accession numbers: HF586251, HF586250, HF586249, HF586248, HE800625

Ilanga discus Herbert, 1987: 302–303, figs 16–20. Type locality: South Africa, Natal, off Durban, 29°53.3’S, 31°11.4’E, 195 m.

Type material. Holotype NM B5905/T3467 (Herbert, 1987).

Material examined. North-Western Madagascar. Chalutages Vauban 1971–1975: stn DC03, 12°36’S, 48°17’E, 300 m, 1 dd sub.—Stn CH 11, 12°40’S, 48°15’E, 375–380 m, 1 dd.—Stn CH 43, 15°25’S, 46°02’E, 250–265 m, 1 lv.—MIRIKY: stn CP3188, 12°31’S, 48°22’E, 298–301 m, 5 lv (DNA samples MNHN 20098758, 20098760, 20098761, 20098776 and 20098777).

Distribution. South Africa, KwaZulu-Natal, 165–270 m (lv); North-Western Madagascar, 265–375 m, lv at 265– 298 m.

Description (supplementary—based on the original description and DNA samples studied). Shell: Moderately to rather tall for genus (H up to 6.8 mm, W to 13.1 mm), height 0.47–0.61×width, about 1.7×aperture height; much wider than high, shape sublenticular, thin-shelled, glossy; spire depressed, periphery subangular; umbilicus very broad, deep. Protoconch ca. 250–300 μm wide, 1.25 whorls, rounded, with about 5 weak spiral and with ter- minal lip slightly expanded. Teleoconch up to 4.8 weakly convex to nearly flat whorls, without shoulder; whorls smooth except first whorl; weak growth lines on last whorls. Suture impressed, not canaliculated. First whorl convex, sculptured with 5–6 spiral cords appearing immediately; cords more or less equally spaced; abapical cords vanishing near end of whorl; very fine axial threads between cords. At end of second whorl, all cords vanished and axial threads disappearing, leaving surface nearly smooth with weak, fine prosocline growth-lines. On last whorl, some very weak, low, thin abapical cords near periphery. Aperture subcircular; peristome incomplete; outer and inner lip thin; inner lip with weak basal thickening against umbilical rim. Base moderately convex, smooth. Umbilicus broad (diameter 25–28% of shell width), central, with perspective to apex, with angulate rim; steep-sided wall with very thin axial threads and without spiral cords inside; axial pleats visible on early whorls, but not body whorl.

Colour: Teleoconch white to yellowish-white, with brown zig zag radial bands (sometimes diffuse) forming usually two distinct spiral bands; base pale or white, with similar zig zag bands.

Operculum: Corneous, multispiral with central nucleus, brown.