Ilanga herberti, Vilvens & Williams, 2020

Vilvens, Claude & Williams, Suzanne T., 2020, New species of Ilanga (Gastropoda: Trochoidea: Solariellidae) from the Indo-West Pacific, Zootaxa 4732 (2), pp. 201-257 : 213-215

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.

Figures

FIGURE 4. A–F. Ilanga laevissima (Martens, 1881), South Africa, Cape Province, NMDP (Africana). NMSA V3139, Stn A 18178 D, 115 m. A–F. 8.5×12.3 mm. A–C. Shell, apertural, apical and basal views. D. Details of protoconch and first whorl. Scale 100 μm. E. Sculpture on whorls. Scale 1 mm. F. Details of umbilical area. Scale 1 mm. G–I. Holotype Trochus laevissimus ZMB/Moll 29315, S. Africa Gazelle 50 fms. J–L. Ilanga 18. South Africa, Cape Province, NMDP (Africana). NMSA V3139, Stn A 18178 D, 115 m. Although morphologically similar to I. laevisissima, this species is genetically distinct. 4.9×7.0 mm. Scale (except SEM images) 5 mm.

FIGURE 5. Ilanga discus Herbert, 1987, North-Western Madagascar. A–I. Madagascar, MIRIKY, stn CP3188, 298–301 m. A–F. MNHN IM-2009-8760, 5.2×8.5 mm. A–C. Shell, apertural, apical and basal views. D. Details of protoconch and first whorl. Scale 100 µm. E. Sculpture on whorls. Scale 1 mm. F. Details of umbilical area. Scale 1 mm. G–I. MNHN IM-2009- 8777, 6.8×11.6 mm. J–L. Vauban 1971–1975, stn CH43, 250–265 m, 6.1×13.1 mm. Scale (except for SEM images) 5 mm

FIGURE 7. Ilanga herberti n. sp., Mozambique Channel, MAINBAZA, stn CP3143, 264–277 m. A–F. Holotype MNHN IM- 2009-15174, 5.6×8.3 mm. A–C. Shell, apertural, apical and basal views. D. Details of protoconch and first whorl. Scale 100 µm. E. Sculpture on whorls. Scale 200 µm. F. Details of umbilical area. Scale 1 mm. G–I. Paratype 1 MNHN IM-2000-34396, 8.8×13.3 mm. Scale (except for SEM images) 5 mm.