Ilanga biradiatula ( Martens, 1902 )

Vilvens, Claude & Williams, Suzanne T., 2020, New species of Ilanga (Gastropoda: Trochoidea: Solariellidae) from the Indo-West Pacific, Zootaxa 4732 (2), pp. 201-257 : 211-213

Ilanga biradiatula ( Martens, 1902)

( Figs 6 A–O, Key 1: 2)

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

COI sequence data: GenBank Accession numbers: HF586276 , HF586275 , HF586274 , HE800624

Solariella biradiatula Martens, 1902: 242 . Type locality: off Dar-es-Salaam, 6°39’S, 39°30’E, about 400 m.

Solariella (Microgaza) meyeri Kilburn, 1973: 560 , figs Id, 2c, 3a, b, 4a. Type locality: off Tugela River mouth (about 29°11’S), 75 fathoms (137 m).

Ilanga biradiatula — Herbert 1987: 299–301 , figs 11–15.

Type material. Three specimens at ZMB were found to match the original description as suggested by Herbert (1987), and are here considered syntypes of Solariella biradiatula ( ZMB / Moll 59917, Dar es Salaam Valdivia, R 243, 400m). We have chosen the only specimen with preserved coloration ( Fig. 6 M–O) to be the lectotype .

Material examined. Mozambique Channel. MAINBAZA: stn CP3135, 25°13’S, 35°18’E, 480–503 m, 13 lv, 5 sub lv ( MNHN IM-2009-8740, IM-2009-8741, IM-2009-8743) . — Stn CP 3136, 25°12’S, 35°17’E, 503–505 m, +/- 25 lv, 5 sub lv . — Stn CC 3142, 23°31’S, 35°50’E, 446–475 m, +/-35 lv, 5 sub lv . — Stn CC 3163, 24°09’S, 35°42’E, 406–410 m, 1 dd sub . — Stn CC 3164, 24°13’S, 35°42’E, 505–506 m, +/-60 lv, +/-10 sub lv.— Local dragging, Bazaruto Is., 90 m, 1 lv . — Madagascar. Chalutages Vauban 1971–1975: stn CH 02, 15°53’S, 48°09’E, 480–520 m, 4 lv . — Stn CH 122, 12°43’S, 48°12’E, 500 m, 2 lv . —MIRIKY: stn CP3184, 12°40’S, 48°12’E, 492–524 m, 1 lv ( MNHN IM-2009-8759).— South Africa. Local dragging, Agulhas Bank, 100 m, 1 lv

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Distribution. From Tanzania to South Africa (Transkei), 90–505 m (lv) (data from Herbert’s study and the new samples of this study).

Description (supplementary—based on the original description and DNA samples studied). Shell: rather tall for genus (H up to 11.6 mm, W to 16.2 mm), wider than high, shape conical to slightly cyrtoconoidal, thinshelled, glossy; spire moderately depressed, height 0.59×to 0.77×width, about 1.7×aperture height; periphery subangular; umbilicus rather broad, deep. Protoconch ca. 250–300 μm wide, 1.25 whorls, rounded, with about 4 very weak spiral cords and a straight, poorly visible terminal lip. Teleoconch up to 5.5 moderately convex whorls with weak subsutural ramp on first whorls but vanishing on last whorls; early whorls with 5 equally spaced spiral cords of similar size, except adapical cord which quickly becomes stronger; antepenultimate whorl with single, strongly granular adapical cord at rim of subsutural ramp; last whorl smooth; weak growth lines on last whorls. Suture impressed, not canaliculated. First whorl convex, sculptured with 5 spiral cords appearing immediately after protoconch; cords more or less equally spaced; P1 at rim of subsutural ramp; axial, weakly prosocline, very fine threads between cords. At end of second whorl, P1 and P2 subgranular to granular, giving a coronate shape to subsutural area; other cords more or less smooth; rather thick axial threads from suture beyond P2. On third whorl, P1 thick- er than other cords, granular beads more flattened, adjoining and axially elongated, transforming into subsutural pleats; P2 still only subgranular; distance between P1 and P2 greater than distance between other cords. On fourth whorl, all cords becoming very weak, low, smooth cords except subsutural P1. On last whorl, almost all cords vanishing except P1 and most abapical cords, leaving weak, smooth, low cords; subsutural pleats vanishing near end of whorl. Aperture subcircular; peristome incomplete; outer and inner lip thin; inner lip with basal thickening against umbilical rim. Base moderately convex, with up to 10 outer smooth, weak, low spiral cords thinner and more closely packed than cords of last whorls; median area nearly smooth; 30–40 axial pleats on intern part reaching umbilical rim, with up to 5 spiral cords making a reticulate pattern. Umbilicus broad (diameter 20–25% of shell width), central, with perspective to apex, with angulate rim bordered by axial pleats of base; convex wall with thin axial threads extending those of centre of base and 4–7 thin spiral cords.

Colour: Teleoconch light brown, possibly with variable axial brown flames; base yellowish white; possible blue-green iridescence; protoconch white.

Operculum: Corneous, multispiral with central nucleus, brown.

Figures

FIGURE 6. Ilanga biradiatula (Martens, 1902). A–F. MNHN IM-2009-8759, Madagascar, MIRIKY, stn CP3184, 492–524 m, 7.4×11.8 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–L. Mozambique Channel, MAINBAZA, stn CP3135, 480–503 m. G–I. MNHN IM-2009-8740, 8.0×13.2 mm. J–L. 9.2×15.5 mm. M–O. Lectotype of I. biradiatula. ZMB/Moll 59917, Dar es Salaam Valdivia, R243, 400m. Scale (except for SEM images) 5 mm.