Vanitrochus Iredale 1929

Genus Vanitrochus Iredale, 1929 Vanitrochus Iredale, 1929a: 272, 294. Type species Solariella tragema Melvill & Standen, 1897 (original designation), Recent, New Caledonia. Diagnosis Shell very small (height up to 3.0 mm), elevated turbiniform, whorls rounded or weakly shouldered; sculpture of spiral cords crossed by axial riblets producing fine, regular cancellation; umbilicus open, margin rounded, funicle lacking; outer lip simple, its interior smooth. Operculum corneous, multispiral, but outer whorls relatively broad and with long growing margin; peripheral fringe broad, with well-developed radial striation; spiral microsculpture distinct. Rachidian and lateral teeth with laterally rounded, extensively overlapping base-plates; inner marginal tooth transitional, lacking cusp; cusps of marginals 2–5 large, somewhat palmate, with ±5 slender, acuminate denticles, middle one slightly larger. Remarks Two species of Vanitrochus occur in New Caledonia. Whilst they are similar, they can be readily distinguished using shell characters (details given below). Vanitrochus tragema is usually found in the more sandy portions of the lagoon nearer to the barrier reef, whereas V. semiustus (Fischer, 1879) is more frequent in muddy and silty environments in the nearshore parts of the lagoon and near mangrove habitats at river mouths. They have not been found alive at the same sampling stations. Both exhibit a strong ‘swimming’ escape response. Vanitrochus species are infaunal, and are able to burrow rapidly into the soft surface sediment layer. Hickman (2008) documented an undescribed tropical Western Australian Vanitrochus species living in coarse grained skeletal carbonate substrata, feeding by epipsammic browsing on the microbiome coating the sediment grains. Two species currently referred to Conotalopia Iredale, 1929 may also ultimately prove to belong to Vanitrochus – Conotalopia ornata (G.B. Sowerby III, 1903) and C. singaporensis (Pilsbry, 1889). They show little resemblance to the type species of Conotalopia, Minolia henniana Melvill, 1891 (Fig. 78H–K).