Ilanga helicoides, 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 : 247-249

Ilanga helicoides n. sp.

( Figs 25 A–O, Table 16, Key 2: 16)

DNA ref: Ilanga 20 ( Williams et al. 2013; Sumner-Rooney et al. 2016)

16S sequence data: GenBank Accession Number: HF585955

Type material. Holotype (4.9× 9.2 mm) MNHN IM-2009-13307 . Paratypes: 4 MNHN IM-2007-18536 , MNHN IM-2000-34410) and 1 NHMUK 20190464 (as listed below) .

Type locality. Solomon Islands, East Rendova Island , SALOMON 1, stn CP2287, 8°41’S, 157°25’E, 253–255 m.

Material examined. Solomon Islands. SALOMON 1: stn DW1776, 08°21’S, 160°41’E, 295–381 m, 1 dd . — Stn DW 1768, 08°21’S, 160°42’E, 194–286 m, 4 lv, 5 dd sub, 1 juv sub . — Stn DW 1834, 10°12’S, 161°18’E, 225–281 m, 8 lv, 6 dd sub . — Stn DW 1835, 10°10’S, 161°24’E, 464–482 m, 1 lv . —SALOMON 2: stn DW2169, 09°01’S, 159°06’E, 100–200 m, 3 dd, 2 dd sub . — Stn DW 2191, 08°23’S, 159°27’E, 300 m, 1 dd . — Stn CP 2193, 08°24’S, 159°27’E, 362–432 m, 1 dd . — Stn DW 2192, 08°24’S, 159°27’E, 335–432 m, 1 dd . — Stn CP 2287, 8°41’S, 157°25’E, 253–255 m, 40 lv (with holotype MNHN IM-2009-13307 , 1 paratype MNHN IM-2007-18536 , 3 paratypes MNHN IM-2000-34410 and 1 paratype NHMUK 20190464 ), 10 lv sub . —SALOMONBOA 3: stn DW2811, 09°42’S, 161°30’E, 228–238 m, 1 dd, 1 juv sub . — Stn DW 2829, 10°46’S, 162°20’E, 220–292 m, 1 dd, 7 dd sub, 2 juv sub . — Stn CP 2834, 10°44’S, 162°21’E, 545–753 m, 1 dd.— Stn DW 2856, 09°45’S, 160°50’E, 206–276 m, 1 dd

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Distribution. Solomon Islands, 200–545 m, lv at 255– 464 m.

Diagnosis. A medium-sized Ilanga species with a depressed, conical spire, a subangulate periphery, weakly convex to almost flat whorls, 4 spiral cords on first whorl, no subsutural pleats; umbilicus very broad, subangulate with a weak spiral cord at rim, without axial pleats around it and 2–3 smooth thin spiral cords in adapical part of umbilical wall.

Description. Shell: Medium size for genus (H up to 5.7 mm, W up to 10.5 mm), wider than high, conical to slightly coeloconoidal, glossy; spire rather depressed, height 0.48×to 0.59×width, about 1.47×to 2.00×aperture height; periphery weakly subangulate; umbilicus very broad and deep. Protoconch ca. 280 μm wide, 1.25 whorls, rounded, with 3 thin, evenly spaced, spiral cords and with a straight, slightly expanded terminal lip. Teleoconch consisting of up to 4.7 weakly convex to almost flat whorls with a weak subsutural ramp on first whorls but vanishing on last whorls; no subsutural pleats; early teleoconch whorls with 4–5 smooth spiral cords, quickly vanishing; last whorls smooth with hardly visible spiral threads near periphery. Suture canaliculated on first whorls, impressed on last whorls. First teleoconch whorl convex, sculptured with 3 smooth spiral cords appearing immediately, usually P1 after half of whorl (absent on some samples); P1 weakest, indistinct; P2 strongest, situated at edge of subangulate subsutural ramp; thin axial threads between cords. On second whorl, P1 (if present) gradually disappearing after half whorl, P2 and P3 vanishing simultaneously somewhat later, P4 disappearing under next whorl; subsutural ramp disappearing before end of whorl. On third teleoconch whorl, narrow translucent subsutural spiral band appearing. Last whorls largely smooth with some faint spiral cords, at periphery. Aperture rounded triangular; peristome incomplete; outer and inner lip thin; inner lip without obvious thickening against umbilical rim. Base convex, smooth, without axial pleats around umbilicus and with a thin, weak spiral cord bordering umbilical rim. Umbilicus very broad (diameter 30–38% of shell width), central, with perspective to apex, with subangulate rim; slightly convex umbilical wall with 2–3 smooth thin spiral cords in adapical part, occasionally with a few spiral cords in its abapical part, without axial threads; axial pleats present on umbilical shell walls of adapical whorls.

Colour: Teleoconch nacreous white with 3 brown, brownish orange or pinkish brown chevron patterned bands, median band narrower; base paler with an external band of regular brownish patches.

Operculum: Corneous, multispiral with central nucleus, light brown.

Remarks. Ilanga helicoides n. sp. is similar to I. lauensis from Fiji, but I. lauensis is not as depressed (height 0.52×to 0.58×width, instead of height 0.48×to 0.59×width here) and is more conical in shape, has additional spirals cords (Si) on the second whorl and has a narrower umbilicus (at most 25% of the shell width).

Etymology. Spiral shaped (Ancient Greek: έλιχοειδής, ές)—with reference to spiral shape of the shell from abapical view.

Figures

FIGURE 25. Ilanga helicoides n. sp., Solomon Islands. A–L. SALOMON 2, stn CP2287, 253–255 m. A–F. Holotype MNHN IM-2009-13307, 4.9×9.2 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. Paratype 1 MNHN IM-2007-18536, 4.7×9.7 mm. J–L. Paratype 2 MNHN IM-2000-34410, 5.7×10.5 mm. M–O. SALOMONBOA 3, stn DW2829, 220–292 m, 5.2×10.4 mm. Scale 5 mm.