Ilanga oxeia, 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 : 236-238

Ilanga oxeia n. sp.

( Figs 19 A–O, Table 10, Key 2: 7)

DNA ref: Ilanga 3 & 15 ( Williams et al. 2013; Sumner-Rooney et al. 2016)

COI sequence data: GenBank Accession numbers: Ilanga 3, HF586253 ; Ilanga 15, HF586252 .

Type material. Holotype (6.6× 10.8 mm) MNHN IM-2007- 18301 . Paratypes: 3 MNHN IM-2000-34402 , MNHN IM-2000-34403, MNHN IM-2009-15196) and 1 NHMUK 20190462 (as listed below) ,

Type locality. Vanuatu, Maio , BOA 1, stn CP2413, 15°42’S, 167°02’E, 268–445 m.

Material examined. Vanuatu. BOA1: stn CP2413, 15°42’S, 167°02’E, 268–445 m, 1 dd (holotype MNHN IM-2007-

18301).— Solomon Islands.SALOMON 1: stn DW1762, 08°40’S, 160°04’E, 396–411 m, 1 dd, 1 dd sub, 1 juv sub . — Stn CP 1836, 10°10’S, 161°22’E, 439–486 m, 1 dd. SALOMON 2: stn CP2260, 08°04’S, 156°55’E, 399–427 m, 1 dd . — Stn CP 2261, 08°02’S, 156°54’E, 433–470 m, 1 dd . —SALOMONBOA 3: stn CP2809, 09°19’S, 161°27’E, 788–1042 m, 1 dd sub . — Stn CP 2814, 09°45’S, 161°32’E, 375–431 m, 3 lv (with paratype 1 MNHN IM-2000-34402 & paratype NHMUK 20190462 ) . — Stn DW 2853, 09°47’S, 160°54’E, 264–285 m, 1 lv, 2 dd sub, 1 dd juv (with paratype 2 MNHN IM-2000-34403) .— Papua New Guinea. BIO-

PAPUA, stn CP3759, 04°00’S, 153°36’E, 287–352 m, 1 lv (paratype 3 MNHN IM-2009-15196).

Distribution. Vanuatu, 268–445 m (lv); Solomon Islands, 285–788 m, lv at 285–375 m and Papua New Guinea, 287– 352 m.

Diagnosis. A medium to rather large Ilanga species with a moderately depressed, conical spire, a slightly subangulate periphery, 5 spiral cords on first teleoconch whorl vanishing on third whorl, subsutural pleats and folds on median whorls, an angulate umbilicus bordered by several spiral cords and 25–35 axial grooves forming a reticulate pattern in the inner third of the base, 5–8 smooth spiral cords and axial threads inside.

Description. Shell: Medium to tall size for genus (H up to 8.7 mm, W up to 14.1 mm), much wider than high, shape conical with large apical angle, glossy; spire moderately depressed, height 0.61–0.63×width, about 1.71×to 1.89×aperture height; rounded to very slightly subangulate periphery; umbilicus very broad and deep. Protoconch ca. 250–350 μm wide, 1.25 whorls, rounded, translucent, with a straight terminal lip. Teleoconch up to 4.4 slight- ly convex whorls; early whorls with 5 spiral cords; intermediate whorls with subsutural axial pleats; last whorls smooth with faint spiral cords on periphery. Suture canaliculated on first whorls, impressed on last whorls. First teleoconch whorl convex, with 5 spiral cords appearing immediately and thin axial threads; P2 strongest, P1 almost as strong as P2, other cords P3, P4 and P5 slightly thinner; distance between cords about 1×to 1.5×width of cords. second whorl, all cords widening and flattening after half whorl; low axial pleats appearing, covering adapical third of whorl; S2 and S3 appearing on some specimens; axial threads disappearing. On third whorl, 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, except a few very weak spiral cords on periphery in some specimens. Aperture subelliptical quadrate; peristome incomplete; outer and inner lip thin; inner lip without thickening against umbilical rim. Base convex; two outer thirds smooth, inner third with reticulate pattern of 2–6 spiral cords and axial grooves on inner third; about 25–35 axial pleats reaching spiral cord bordering umbilical rim. Umbilicus broad (diameter 18–25% of shell width), central, with perspective to apex, with angulate rim, convex wall, axial threads and 5–8 spiral cords forming reticulate pattern inside.

Colour: Teleoconch pinkish nacreous white, with axial brownish orange flames; base paler, without maculations.

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

Remarks. Only two specimens were sequenced for this species; one from Papua New Guinea and one from Vanuatu. These two specimens were treated as separate ESUs by Williams et al. (2013) ( Ilanga 3 and Ilanga 15), however they are genetically similar and it was not possible to separate them on morphological characters. We include in this species samples from the Solomon Islands based on their morphological similarity to sequenced specimens. A similar distribution range has been seen in other solariellids, which likewise demonstrate strong genetic structure among populations ( Williams et al. 2013), however future studies are needed to determine whether there are in fact two species.

Among Ilanga species having both spiral cords and axial threads inside the umbilicus, I. oxeia can be compared to I. harrytaylori from the New Caledonia-Tonga area and to I. eurystoma from Papua New Guinea. The new species differs from these two species by having a more conical shape with almost flat whorls and by the Si not being present simultaneously with the Pi on the first whorl

Moreover, it differs from I. harrytaylori by the much stronger axial threads inside the umbilicus and from I. eurystoma by the slightly subangulate periphery, the reticulate pattern made by spiral cords and axial grooves on the inner third of the base and in having fewer spiral cords inside the umbilicus.

Etymology. Pointed, sharp (Ancient Greek: όξύς, εια, ύ)—with reference to the general shape of the shell.

Figures

FIGURE 19. Ilanga oxeia n. sp. A–F. Holotype MNHN (MNHN IM-2007-18301), Vanuatu, BOA1, stn CP2413, 268–445 m, 6.6×10.8 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–L. Solomon Islands, SALOMONBOA 3. G–I. Paratype 1 MNHN IM-2000-34402, stn CP2814, 375–431 m, 8.5×13.5 mm. J–L. Paratype 2 MNHN IM-2000-34403, stn DW2853, 285–264 m, 8.5×13.7 mm. M–O. Paratype MNHN IM-2009-15196, Papua New Guinea, BIOPAPUA, stn CP3759, 287–352 m, 6.4×10.2 mm.