Ilanga navakaensis ( Ladd, 1982 )

Vilvens, Claude & Williams, Suzanne T., 2020, New species of Ilanga (Gastropoda: Trochoidea: Solariellidae) from the Indo-West Pacific, Zootaxa 4732 (2), pp. 201-257 : 217-218

Ilanga navakaensis ( Ladd, 1982) (new comb.)

( Figs 8 A–I, Table 3, Key 2: 11)

DNA ref: Ilanga 6 ( Williams et al. 2013; Sumner-Rooney et al. 2016)

COI sequence data: GenBank Accession numbers: HF586268 , HF586269 , LT575890

Microgaza (Microgaza) navakaensis Ladd, 1982: 25–26 , pl. 34, figs 1–5. Type locality: Navaka River Pleistocene outcrops, Santo, Vanuatu.

Microgaza navakaensis — Marshall 1999: 32–33 .

Type material. Holotype USNM 250150 ( Ladd 1982).

Material examined. Vanuatu. MUSORSTOM 8: stn DW1105, 15°03’S, 167°08’E, 154–179 m, 6 dd juv . — MUSORSTOM 10: stn DW1384, 18°19’S, 178°06’E, 260–305 m, 9 dd juv . — Stn CP 1390, 18°19’S, 178°05’W, 234–361 m, 1 dd sub . —SANTO 2006: stn AT54, 15°32’S, 167°14’E, 68–79 m, 1 lv (photographed) . — Stn AT 112, 15°34’S, 167°16’E, 150–168 m, 5 lv (with 1 DNA sample MNHN IM-2007-18446) . —Stn unknown, 1 lv (DNA sample MNHN IM-2007-18447).— Tonga Islands. BORDAU 2: stn DW1587, 18°37’S, 173°54’W, 309–400 m, 1 dd .

Distribution. Vanuatu, 79–260 m, lv at 79–150 m; off southern New Caledonia, depth unknown ( Marshall, 1999). Tonga, dd at 309- 400 m.

Description (supplementary—based on the original description and DNA samples studied). Shell: Medium sized Ilanga species (H up to 5.7 mm, W to 9.2 mm), wider than high, shape conical, thin-shelled, glossy; spire rather elevated to moderately depressed, height 0.54–0.66×width, 1.6–2.0×aperture height; periphery subangulate; umbilicus broad, deep. Protoconch ca. 300–320 μm wide, 1.25 whorls, rounded, with about 3 weak spiral cords and a straight, very slightly expanded terminal lip. Teleoconch up to 4.4 moderately convex whorls with weak subsutural ramp on first whorls,vanishing on last whorls; early teleoconch whorls with 5 spiral cords; penultimate whorl with strongly granular subsutural cord; last whorl with about 4 weak, thin spiral threads on abapical half; weak growth lines on last whorls. Suture impressed, not canaliculated. First teleoconch whorl convex, sculptured with P2, P3 and P4 appearing immediately; cords more or less equally spaced, P2 slightly stronger; P1 appears on last third of first whorl, thinner than other cords;, very fine, weakly prosocline axial threads between cords.

S3 appears on second teleoconch whorl; distance between P1, P2 and P3 much greater than distance between other cords; wide, low axial pleats appearing between P1 and P2; other cords more or less smooth. On third whorl, pleats transforming into strong nodules, making a strongly nodular cord and giving a coronate shape to subsutural area; P2 weakening and moving abapically, P3, S3 and P4 still visible; all cords low, smooth. On last whorl, nodular subsutural cord obsolete and finally vanishing, leaving a smooth surface except four abapical, smooth, low cords. Aperture subcircular; peristome incomplete; outer and inner lip thin; inner lip with basal thickening against umbilical rim. Base moderately convex, smooth on outer part, with 30–40 axial pleats on intern third or half, reaching umbilical rim. Umbilicus broad (diameter 24–27% of shell width), central, with perspective to apex, with angulate rim, possibly with a thin smooth spiral cord; vertical wall with about 6 smooth spiral cords.

Colour: Teleoconch light brownish white, last whorls with brown zig zag lines, making distinct subsutural and peripheral areas with chevron shaped lines; base lighter, possibly with zig zag pattern; protoconch whitish.

Remarks. The single Tongan specimen is a little more depressed and has eight spiral cords inside the umbilicus.

Figures

FIGURE 8. Ilanga navakaensis (Ladd, 1982), Vanuatu, SANTO 2006. A–F. MNHN IM-2007-18446, Stn AT112, 150–168 m, 5.0×9.2 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 300 µm. G–I. Stn AT54, 68–79 m, 5.7×8.6 mm. Scale (except for SEM images) 5 mm.