Ilanga eurystoma, 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 : 234-236

Ilanga eurystoma n. sp.

( Figs 18 A–I, Table 9, Key 2: 8)

DNA ref: Ilanga 1 ( Williams et al. 2013; Sumner-Rooney et al. 2016)

COI sequence data: GenBank Accession numbers: HF586246 , HF586247 , LT575886 , LT575888 , LT575887 , LT575889 , MK393380 .

Type material. Holotype (6.3× 10.8 mm) MNHN IM-2009-15197 . Paratype: MNHN IM-2009-15190 .

Type locality. Papua New Guinea, Seamount off Bougainville, BIOPAPUA, stn DW3745, 5°33‘S, 154°00‘E, 369–377 m.

Material examined. Papua New Guinea, Seamount off Bougainville. BIOPAPUA: stn DW3745, 5°33’S, 154°00’E, 369–377 m, 2 lv (holotype MNHN IM-2009-15197, paratype MNHN IM-2009-15190) .

Distribution. Only known from the type locality.

Diagnosis. A medium to rather large Ilanga species with a moderately depressed, conical spire, a rounded periphery, 6 spiral cords on first teleoconch whorl vanishing on third whorl, subsutural pleats and folds on median whorls, a flared aperture, an angulate umbilicus bordered by a granular spiral cord, with 35–45 axial pleats around it, 7–9 smooth spiral cords and thin axial threads inside.

Description. Shell: Tall for genus (H up to 11.4 mm, W up to 16.6 mm), much wider than high, shape conical with large apical angle, glossy; spire rather depressed, height 0.62×to 0.69×width, about 1.58×to 1.90×aperture height; rounded periphery; umbilicus very broad and deep. Protoconch ca. 330 μm wide, 1.25 whorls, rounded, translucent, with 2 very weak spiral cords on abapical part and with a slightly expanded terminal lip. Teleoconch up to 5.4 convex whorls with a weak subsutural ramp on first whorls but vanishing on last whorls; early whorls with 6 smooth spiral cords; intermediate whorls with subsutural axial pleats; last whorls smooth. Suture canaliculated on first whorls, impressed on last ones. First whorl convex, with 6 nearly smooth spiral cords appearing immediately after protoconch and thin axial threads; P2 strongest, P1 almost as strong as P2, other cords P3, S3, P4 and S4 slightly thinner except S4 very thin; subsutural ramp forming at end of whorl, with P1 on rim; distance between cords about 1×to 1.5×width of cords; S4 covered by next whorl at end of whorl. On second whorl, all cords widening and flattening after half whorl; low axial pleats appearing, covering adapical third of whorl; P4 disappearing under next whorl near end of whorl; axial threads no longer visible. On third whorl, subsutural pleats stronger, especially in subsutural area; all spiral cords vanishing. On fourth whorl, axial pleats weakening and vanishing, leaving only a smooth, rather thin, translucent subsutural spiral band. Last whorl completely smooth. Aperture subelliptical, flared; peristome incomplete; outer and inner lip thin; inner lip without thickening against umbilical rim. Base convex; outer two thirds smooth, inner third with about 35–45 axial pleats reaching spiral cord bordering umbilical rim, cord granular at intersection with axial grooves and pleats. Umbilicus broad (diameter 30–33% of shell width), central, with perspective to apex, with angulate rim, convex wall, thin axial threads and 7–9 spiral cords making reticulate pattern inside.

Colour: Teleoconch silver-white or nacreous white, possibly with strong pink-green iridescence and with rather thin axial brown flames.

Operculum: Unknown.

Remarks. Ilanga eurystoma n. sp. is rather close to I. harrytaylori from New Caledonia-Tonga area, but this slightly smaller species (H up to 7.9 mm, W to 13.9 mm) has several faint spiral cords on a subangulate periphery, a S4 present with the other Pi-Si and less numerous spiral cords inside the umbilicus.

Etymology. Flared (Ancient Greek: εύρύστομος, ον)—with reference to the shape of the aperture.

Figures

FIGURE 18. Ilanga eurystoma n. sp., Papua New Guinea, Seamount off Bougainville, BIOPAPUA, stn DW3745, 369–377 m. A–F. Holotype MNHN IM-2009-15197, 11.4×16.6 mm. A–C. Shell, apertural, apical and basal views. Scale 5 mm. 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. Paratype MNHN IM-2009-15190, 8.7×14.0 mm.