Ilanga stephanophora, 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 : 229-231

Ilanga stephanophora n. sp.

( Figs 16 A–P, Table 7, Key 2: 12)

Ilanga 16 & Ilanga 5 ( Williams et al. 2013; Sumner-Rooney et al. 2016)

COI sequence data: GenBank Accession numbers: Ilanga 5, HF586263 , HF586264 , HF586265 , HF586266 ; Ilanga 16, HF586262 .

Type material. Holotype (6.0×10.0 mm) MNHN IM-2009-8801 . Paratypes: 4 MNHN IM-2007-35552, IM-2007- 35578, IM-2007-35579, IM-2007-35584 and 1 NHMUK 20190456 (as listed below) .

Type locality. South-eastern New Caledonia, TERRASSES: stn DW3094, 22°04’S, 167°03’E, 250–300 m.

Material examined. South-eastern New Caledonia. LAGON: stn DW387, 22°39’S, 167°07’E, 220–225 m, 1 lv.—MUSORSTOM 4: stn DW203, 22°36’S, 167°06’E, 105–110 m, 2 dd, 1 juv sub.—Stn DW204, 22°37’S, 167°06’E, 120 m, 1 dd.—BATHUS 2: stn DW716, 22°41’S, 167°12’E, 290–308 m, 1 dd.—Stn DW717, 22°44’S, 167°17’E, 350–393 m, 1 dd.—Stn DW724, 22°48’S, 167°26’E, 344–358 m, 1 dd, 1 dd sub, 5 juv sub.—Stn DW726, 22°47’S, 167°29’E, 241–260 m, 1 dd.—Stn DW746, 22°31’S, 166°25’E, 250 m, 1 dd.—BATHUS 2/ MUSORSTOM 8: No station data (“mélange accidentel”), 10 dd, 3 dd sub, 3 juv sub.—BATHUS 3: stn DW836, 23°02’S, 166°59’E, 295–306 m, 1 lv.—NORFOLK 2: stn DW2040, 23°41’S, 168°01’E, 285 m, 1 dd sub.—Stn CP2119, 23°23’S, 168°02’E, 300 m, 1 dd.—Stn DW2158, 22°41’S, 167°14’E, 265–283 m, 3 dd, 1 dd sub, 1 juv sub.—TERRASSES: stn DW3090, 22°16’S, 167°08’E, 260 m, 4 dd, 1 juv sub.—Stn DW3094, 22°04’S, 167°03’E, 250–300 m, 1 lv (holotype MNHN IM-2009-8801).—EXBODI: stn DW3787, 22°13’S, 167°06’E, 223–249 m, 1 juv sub.—Northern New Caledonia. LAGON: stn DW858, 20°37’S, 165°07’E, 220 m, 1 dd.—Stn BATHUS 4: stn CP897, 20°16’S, 163°52’E, 305–350 m, 1 dd.—Stn DW901, 19°03’S, 163°15’E, 297 m, 1 dd.—CONCALIS: stn CP2961, 19°04’S, 163°11’E, 220–390 m, 9 lv (with paratypes MNHN IM-2007-35552, IM-2007-35578, IM- 2007-35579, IM-2007-35584 and paratype NHMUK 20190456).—EXBODI: stn DW3923, 18°33’S, 164°20’E, 580–703 m, 1 juv sub.—Eastern New Caledonia. BIOGEOCAL: stn DW253, 21°32’S, 166°29’E, 310–315 m, 1 dd sub.—BATHUS 1: stn DW653, 21°17’S, 165°57’E, 190–207 m, 2 dd.—Stn DW666, 20°57’S, 165°34’E, 105–110 m, 1 dd, 2 dd sub, 2 juv sub.—Stn CP668, 20°57’S, 165°35’E, 205–219 m, 1 dd.—Stn DW678, 20°49’S, 165°19’E, 94–100 m, 1 dd, 1 dd sub.—Stn CP680, 20°48’S, 165°18’E, 86–92 m, 1 lv.—Stn DW689, 20°33’S, 165°00’E, 260–265 m, 1 dd.—Stn DW691, 20°35’S, 164°59’E, 227–250 m, 3 dd.—Stn CP712, 21°44’S, 166°35’E, 210 m, 1 lv.— Loyalty Islands. MUSORSTOM 6: stn DW480, 21°08’S, 167°55’E, 350–400 m, 1 dd.—Stn LIFOU 2000: stn DW1650, 20°54’S, 167°02’E, 120–250 m, 5 lv, 2 dd sub, 2 juv lv.— Fiji. MUSORSTOM 10: stn CP1323, 17°16’S, 177°46’E, 143–173 m, 1 dd.—Stn DW1334, 16°51’S, 178°14’E, 251–257 m, 1 dd, 1 dd sub.—Stn DW1384, 18°19’S, 178°06’E, 260–305 m, 12 dd, 5 dd sub, 12 juv sub.—Stn DW1388, 18°19’S, 178°02’E, 313–446 m, 2 dd.—Stn BORDAU 1: stn DW1472, 19°40’S, 178°10’W, 262–266 m, 1 dd.— Futuna Island. MUSORSTOM 7: stn DW513, 14°14’S, 178°11’W, 260–300 m, 1 dd.

Distribution. New Caledonia, 82–580 m, lv at 82–250 m; Loyalty Islands, 250–350 m; Fiji, 173–313 m; Futuna Island, 260– 300 m.

Diagnosis. A medium sized Ilanga species with a moderately depressed, conical spire, a subangulate periphery with some faint spiral cords, 5 spiral cords on first teleoconch whorl and additional cords on second and third whorl, subsutural pleats on median whorls, angulate umbilicus with or without axial pleats around, bordered by a smooth spiral cord at rim and 8–10 spiral cords inside.

Description. Shell: Medium size for genus (H up to 6.0 mm, W up to 10.6 mm), wider than high, conical to slightly coeloconoidal in shape, glossy; spire moderately depressed, height 0.51×to 0.60×width, about 1.70×to 1.92×aperture height; periphery weakly subangulate; umbilicus broad and deep. Protoconch about 350 μm wide, 1.25 whorls, rounded, with 3 thin, evenly spaced, spiral cords and with a straight, slightly expanded terminal lip without varix. Teleoconch up to 4.5 convex whorls with a weak subsutural ramp on first whorls, vanishing on last whorls; early whorls with 5 smooth spiral cords, rapidly ceasing; subsutural axial pleats on intermediate whorls; last whorls smooth with poorly visible spiral threads near periphery. Suture canaliculated on first whorls, impressed on last whorls. First whorl convex, sculptured with 4 smooth spiral cords appearing immediately after protoconch and P1 half a whorl later; P2 strongest, at edge of subangulate subsutural ramp. On second whorl, S1 and S2; P2 much wider but flattening; axial threads becoming quickly flat axial pleats; subsutural ramp weakening; narrow translucent subsutural spiral band appearing at end of whorl. S3 appearing on third whorl; all cords ceasing except S3 and P4; subsutural axial pleats stronger and subsutural ramp vanishing. Last whorls smooth, S3 and P4 as faint spiral cords still poorly visible at periphery. Aperture rounded triangular; peristome incomplete; outer and inner lip thin; inner lip with a weak thickening against umbilical rim. Base convex; weak smooth axial pleats variable: sometimes occurring in inner part of umbilicus, opposite aperture or without distinct pleats on last half, or all around umbilicus or rarely nearly absent; thin spiral cord bordering umbilical rim. Umbilicus broad (diameter 30–32% of shell width), central, with perspective to apex, with angulate rim, with vertical wall, 8 to 10 smooth thin spiral cords inside, sometimes closer to each other in adapical part, and usually without axial threads (rarely very thin and very weak close axial threads on umbilical wall); axial pleats on umbilical shell walls of adapical whorls.

Colour: Teleoconch nacreous white with irregular brownish flames, forming usually a band patterned with subsutural chevrons and often another peripheral band of regular maculations; protoconch off-white.

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

Remarks. Although treated as two evolutionarily significant units (ESUs), Ilanga 5 and Ilanga 16, in Williams et al. (2013) and Sumner-Rooney et al. (2016), these units were not distinguished when using a lower confidence interval to define species boundaries and the estimated time of divergence between these ESUs was low (<1.5 Myr) ( Williams et al. 2013). After examination of more specimens we now believe these two ESUs to belong to a single species.

New Caledonian I. stephanophora n. sp. specimens (n = 52 adults) have two striking features: a high variability regarding the axial pleats around the umbilicus (all around, only on some parts, or even in rare cases, almost absent) and a wide New Caledonian distribution, over a wide range of habitats and depths. The Fijian specimens (n = 17 adults), for which molecular data are lacking, are more constant regarding their conchological features, always having axial pleats all around the umbilicus and 10 spiral cords inside.

The new species weakly resembles I. fulgens from Japan, Taiwan and Philippines, and I. polygramma from Indonesia but these species with a more or less similar size have only 4 primary cords. Moreover, I. fulgens has a more rounded shape and thin axial threads on the whole surface of the whorls while I. polygramma is more depressed.

Etymology. Crowned (Ancient Greek: στεφανηφόρος, ον)—with reference to the subsutural pleats on the in- termediate teleoconch whorls.

Figures

FIGURE 16. Ilanga stephanophora n. sp. A–J. New Caledonia. A–F. Holotype MNHN (IM-2009-8801), TERRASSES, stn DW3094, 250–300 m, 6.0×10.0 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–J. NHMUK 20190456, CONCALIS, stn CP2961, 220–390 m, 5.2×9.8 mm. BATHUS 4, stn CP897, 305–350 m, 4.9 x8.9 mm. K–L. BA- THUS 4, stn CP897, 305–350 m, 4.9×8.9 mm. K. Shell, apertural view. L. Details of umbilicus wall with weak axial threads. M–P. Fiji, MUSORSTOM 10, stn DW1384, 260–305 m, 5.2×8.9 mm.