Ilanga euryomphalos, 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 : 218-220

Ilanga euryomphalos n. sp.

( Figs 9 A–L, Table 4, Key 2: 10)

Type material. Holotype (6.9× 12.6 mm) MNHN (IM-2000-34397) . Paratypes: 2 (MNHN IM-2000-34398; MNHN IM-2000-34399) and 1 NHMUK 20190457 (as listed below) .

Type locality. Vanuatu, MUSORSTOM 8, Stn DW 1094, 15°08’S, 167°12’E, 312–314 m.

Material examined. Vanuatu. MUSORSTOM 8: stn DW1065, 16°16’S, 167°21’E, 360–419 m, 1 dd, 3 dd sub (with paratype 1 MNHN IM-2000-34398) . — Stn DW 1094, 15°08’S, 167°12’E, 312–314 m, 1 dd (Holotype MNHN IM-2000-34397) . — Stn DW 1097, 15°05’S, 167°11’E, 281–288 m, 1 dd sub . — Stn DW 1100, 15°05’S, 167°10’E, 258–265 m, 4 dd sub, 1 dd juv . — Stn DW 1106, 15°05’S, 167°12’E, 305–314 m, 2 dd, 1 dd sub (Paratype 2 MNHN IM-2000-34399 and paratype NHMUK 20190457 ) .— Solomon Islands. SALOMON 1: stn CP1831, 10°12’S, 161°19’E, 135–325 m, 1 sub lv . —SALOMON 2: stn DW2292, 08°43’S, 157°25’E, 165–190 m, 1 juv sub dd . —SA- LOMONBOA 3: stn DW2807, 09°15’S, 161°24’E, 504–617 m, 1 dd sub .

Distribution. Vanuatu, 265–360 m (dd); Solomon Islands, 190–504 m, lv at 135– 325 m.

Diagnosis. A medium sized Ilanga species with a depressed, more or less conical spire, a weakly subangular periphery, 5 spiral cords on first whorl, subsutural pleats on third whorl, very broad angulate umbilicus with about 35–40 strong axial pleats all around, bordered by a thin spiral cord at rim and 6–8 spiral cords inside.

Description. Shell: Rather large size for genus (H up to 6.9 mm, W to 12.6 mm), much wider than high, shape conical to slightly cyrtoconoidal, thin-shelled, glossy; spire depressed, height 0.47×to 0.55×width, 1.8×to 2.3×aperture height; periphery subangulate; umbilicus very broad, deep. Protoconch ca. 250–30 μm wide, 1.25 whorls, rounded, with a poorly visible, straight terminal lip. Teleoconch up to 4.7 moderately convex whorls with weak subsutural ramp on first whorls, vanishing on last whorls; second whorl with 5 spiral cords; third whorl with a nodular subsutural cord; lasts whorls smooth. Suture impressed, not canaliculated. First teleoconch whorl convex, sculptured with P2, P3 and P4 appearing immediately; cords more or less equally spaced; P1 at middle of whorl, usually thinner; very fine, weakly prosocline axial threads between cords, becoming rapidly obsolete at end of the whorl. On second teleoconch whorl, all cords vanishing, P2 last to vanish; low axial pleats appearing on second half whorl. On third whorl, pleats resolving into strong nodules, making a strongly nodular cord and giving a coronate shape to subsutural area. On next whorl, nodular subsutural cord vanishing, leaving a nearly smooth surface with a microsculpture of faint spiral and axial threads on periphery. Aperture subcircular; peristome incomplete; outer and inner lip thin; inner lip with basal weak thickening against umbilical rim. Base moderately convex, smooth on outer part, with 35–40 axial pleats on intern third or half, reaching umbilical rim. Umbilicus very broad (diameter 24–32% of shell width), central, with perspective to apex, with an angulate rim and a rather strong, crenelated spiral cord; convex wall with about 6 smooth spiral cords, cords more visible on adapical part.

Colour: Teleoconch light brownish white, last whorls with brown zig zag lines and larger patches, making at least one distinct area with chevron shaped lines above periphery; base lighter, with brown patches; protoconch whitish.

Remarks. The new species is rather close to I. navakaensis from Vanuatu and New Caledonia, but I. navakaensis is smaller and has a more elevated spire, a S3 spiral cord, a stronger spiral cord at the umbilical rim and thinner chevron-like lines on the last whorls.

In the specimens from the Solomon Islands, the subsutural pleats appear earlier (second teleoconch whorl) and vanish later (end of third teleoconch whorl).

Etymology. Wide (Ancient Greek: εύρύς, εϊα, ύ) and—navel, umbilicus (Ancient Greek: όμφαλόϛ, ού - masc.)— used as a noun in apposition—with reference to the very large umbilicus of the shell.

Figures

FIGURE 9. Ilanga euryomphalos n. sp. A–H. Vanuatu, MUSORSTOM 8. A–D. Holotype MNHN IM-2000-34397, stn DW1094, 312–314 m, 6.9×12.6 mm. E–H. Paratype MNHN IM-2000-34398, stn DW1106, 305–314 m, 5.6×11.8 mm. I–L. Solomon Islands, SALOMON 1, stn CP1831, 135–325 m 5.1×10.6 mm. Scale 5 mm.