Ilanga herberti Vilvens & Williams 2020, n. sp.
Creators: name: Vilvens, Claude
name: Williams, Suzanne T.
Publisher: name: Zenodo
Year: 2020
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Gastropoda
Trochida
Solariellidae
Ilanga
Ilanga herberti

description: Ilanga herberti n. sp.
(Figs 7 A–I, Table 2, Key 1: 3)
Ilanga 11 (Williams et al. 2013; Sumner Rooney et al. 2016)
16S sequence data: GenBank Accession numbers: HF585956
Type material. Holotype (5.6× 8.3 mm) MNHN (IM-2009-15174, lv). Paratypes: 2 MNHN (IM-2000-34396, lv) (as listed below).
Type locality. Mozambique Channel, MAINBAZA, stn CP3143, 23°32‘ S, 35°46‘ E, 264–277 m.
Material examined. Mozambique Channel. MAINBAZA: stn CP3143, 23°32‘S, 35°46‘E, 264–277 m, 3 lv, 1 dd sub (with holotype MNHN IM-2009-15174, 2 paratypes MNHN IM-2000-34396).
Distribution. Only known from the type locality.
Diagnosis. A medium sized Ilanga species with a moderately elevated, conical to slightly coeloconoidal spire, a rounded periphery with very convex whorls, 5 strong spiral cords on early teleoconch whorls, no subsutural pleats, umbilicus with rounded rim, without axial pleats around it and 6–8 spiral cords inside.
Description. Shell: Rather tall for genus (H up to 8.8 mm, W to 15.3 mm), wider than high, shape conical to slightly coeloconoidal, thin-shelled, glossy; spire moderately depressed, height 0.66×to 0.67×width, 1.97×to 2.1×aperture height; rounded periphery; umbilicus very broad, deep. Protoconch ca. 250 μm wide, 1.25 whorls, rounded, with about 5 very weak spiral and without visible terminal lip. Teleoconch up to 5.4 convex whorls with a very weak subsutural ramp on first whorls but vanishing on last whorls; early whorls with 5 equally spaced spiral cords of similar size; last whorls almost smooth, with only very weak, thin spiral threads on abapical half. Suture impressed, not canaliculated. First whorl convex, sculptured with 5 strong spiral cords appearing immediately after protoconch; cords nearly smooth to weakly subgranular, more or less equally spaced; P1 at rim of a weak subsutural ramp; axial, weakly prosocline, very fine threads between cords. At end of second whorl, all cords more or less smooth, weakening near end of whorl; axial threads weakening and vanishing at end of whorl. On third whorl, all cords disappeared, whole surface becoming smooth, except some very weak, very thin, poorly visible spiral threads. On last whorls, spiral threads more numerous but still very hard to recognize, more distinct on abapical part and especially on periphery. Aperture subcircular; peristome incomplete; outer and inner lip thin; no thickening towards umbilical rim. Base moderately convex, smooth. Umbilicus very broad (diameter about 25% of shell width), central, with perspective to apex, with rounded rim, without axial pleats around it; convex wall with very thin axial threads and 6–10 thin spiral cords.
Colour: Teleoconch greyish white with prosocline brown flames; base whitish; protoconch whitish brown.
External anatomy: Small tubercles on tentacles. Operculum corneous, multispiral with central nucleus, light brown.
Remarks. Ilanga herberti n. sp. weakly resembles I. laevissima (Martens, 1881) (Figs 4 A–L) from South Africa, but the two are genetically distinct (based on 16S sequence data from Williams et al. 2013). Morphologically I. laevissima is larger (H up to 15 mm, W to 22 mm), has less convex whorls, only very weak spiral cords on the early teleoconch whorls (vs well-defined, equally-sized cords in I. herberti) and thin axial threads inside the umbilicus (no spiral threads in I. herberti).
The new species may be compared to I. discus Herbert, 1987 (Figs 5 A–L) from eastern South Africa and North- Western Madagascar, but I. discus is slightly smaller and more depressed (height 0.47–0.61×width, instead of height 0.66–0.67×width in I. herberti, the difference being statistically significant (t = -5.4512, df = 5.7104, p-value = 0.001859—t-test performed with R software).
Ilanga discus has flattened whorls, spiral cords are developed up to the third teleoconch whorl. Moreover, I. discus has an umbilicus bordered by an angular rim and lacks spiral cords within the umbilicus.
The new species is rather similar to I. lirellata Herbert, 1987 from eastern South Africa, but this much smaller species has a more elevated spire, a wider protoconch and axial pleats around the umbilical rim.
Ilanga herberti n. sp. closely resembles I. maculicincta Herbert, 1987 and I. polita Herbert, 1987, both from eastern South Africa, but these much smaller (H up to 6.8 mm, W up to 8.6 mm and H up to 3.8 mm, W up to 4.9 mm respectively) species have a more elevated spire, a much wider protoconch (both 460–500 µm) and a narrower umbilicus (about 15% and 18% respectively).
Etymology. Named after David “Dai” G. Herbert (KwaZulu-Natal Museum, former NMSA) in recognition of the numerous valuable malacological works he has produced in systematics, especially about the molluscan fauna of South Africa and adjacent area of south-western Indian Ocean.
description: Published as part of Vilvens, Claude & Williams, Suzanne T., 2020, New species of Ilanga (Gastropoda: Trochoidea: Solariellidae) from the Indo-West Pacific, pp. 201-257 in Zootaxa 4732 (2) on pages 213-215, DOI: 10.11646/zootaxa.4732.2.1, http://zenodo.org/record/3663329