Vanitrochus semiustus ( Fischer, 1879 )

Herbert, David G., 2024, The Umboniinae (Mollusca: Gastropoda: Trochidae) of New Caledonia, with descriptions of two new genera and eight new species, plus an additional new species from the Bismarck Sea, European Journal of Taxonomy 973, pp. 1-143 : 122-127

Vanitrochus semiustus ( Fischer, 1879)

Figs 68–70 , 71A , 72A, C–D

Trochus (Minolia) semiustus Fischer, 1879: 23 . Type locality: Ouagap and Kua-Kue, Grande Terre, New Caledonia.

Trochus (Minolia) semiustus – Fischer 1886: 73, pl. 1 fig. 6.

Monilea (Minolia) semiusta – Pilsbry 1889 –90: 270, pl. 41 fig. 36.

Vanitrochus semiustus – Iredale 1929a: 272, 295. — Alldredge & King 1977.

Material examined

Syntypes

NEW CALEDONIA – Grande Terre • 30 specimens, Ouagap and Kua-Kue; MNHN-IM-2000-31305. (https://science.mnhn.fr/institution/mnhn/collection/im/item/2000-31305)

Other material

NEW CALEDONIA – Grande Terre, Ouégoa • 1 specimen, living; LPR-NC Diahot, Stn KD589; 20°16.5′ S, 164°17.7′ E; depth 1 m; 23 Nov. 2019; KOUMAC 2.3 leg.; sédiment sombre sablo-vaseux à Halophila ; DNA voucher; MNHN-IM-2019-10162 • ± 100 specimens, living; environs of Diahot estuary, Stn KD590; 20°16.6′ S, 164°18.2′ E; depth 1 m; 23 Nov. 2019; KOUMAC 2.3 leg.; sédiment sombre sablo-vaseux à Halophila ; MNHN • 4 specimens, living; LPR-NC Diahot estuary, Stn KR981; 20°16.9′ S, 164°18.3′ E; depth unknown; 22 Nov. 2019; KOUMAC 2.3 leg.; DNA vouchers; MNHN- IM-2019-10140 (image PM832 ), -10143, -10144 and -10145 . – Grande Terre, Koumac • 17 specimens, dead; Paagoumène, Stn 1289; 20°29.2′ S, 164°10.2′ E; 0 m; Oct. 1993; Expédition Montrouzier leg.; marée, platier avec blocs; MNHN • 2 specimens, living; Stn KD539; 20°34.1′ S, 164°10.6′ E; depth 11 m; 6 Nov. 2019; KOUMAC 2.3 leg.; algues brunes, éponges; MNHN • 2 specimens, dead; Stn KD556; 20°32.9′ S, 164°12.2′ E; depth 5–6 m; 11 Nov. 2019; KOUMAC 2.3 leg.; sable gris; MNHN • 1 specimen, dead; Stn KB629; 20°35.5′ S, 164°12.9′ E; depth 10 m; 7 Nov. 2019; KOUMAC 2.3 leg.; patch corallien de fond sableux lagonaire; MNHN • 3 specimens, living; Stn KS510; 20°34.3′ S, 164°13.5′ E; depth 10 m; 6 Nov. 2019; KOUMAC 2.3 leg.; dalle ensablée à gorgones, caulerpes, de lagon; MNHN • 1 specimen, dead; Stn KD505; 20°34.3′ S, 164°15.2′ E; depth 2 m; 29 Oct. 2019; KOUMAC 2.3 leg.; sablo-vaseux coquillé; MNHN • 1 specimen, dead; Chenal de la Passe de Koumac, Stn 1314; 20°39.8′ S, 164°15.3′ E; depth 30–63 m; Oct. 1993; Expédition Montrouzier leg.; sable coquillier vaseux; MNHN • 1 specimen, living; Stn KD548; 20°40.3′ S, 164°15.7′ E; depth 11 m; 10 Nov. 2019; KOUMAC 2.3 leg.; sable gris et éponges; DNA voucher, photographed alive (image LC474 ); MNHN- IM-2019-8510 • 100+ specimens, living; Anse de Koumac [Baie de Ouanap], Stn 1277; 20°34.0′ S, 164°16.0′ E; depth 0–2 m; Oct. 1993; Expédition Montrouzier leg.; fonds meubles, herbiers; MNHN • 5 specimens, dead; Anse de Koumac [Baie de Ouanap], Stn 1278; 20°34.0′ S, 164°16.0′ E; depth 0–2 m; Oct. 1993; Expédition Montrouzier leg.; fonds durs; MNHN • 7 specimens, living; Koumac [Pandop] marina, Stn KS513; 20°34.9′ S, 164°16.4′ E; depth 4 m; 18 Nov. 2019; KOUMAC 2.3 leg.; vase; DNA vouchers; MNHN-IM-2019-9565 (image PM710 ) and -9566 • 1 specimen, living; Stn KB667; 20°39.5′ S, 164°17′ E; depth 1 m; 22 Nov. 2019; KOUMAC 2.3 leg.; herbier de phanérogames sur platier sableux de récif intermédiaire; DNA voucher; MNHN-IM-2019-10142 • 11 specimens, living; Stn KD557; 20°41.4′ S, 164°17.1′ E; depth 4–5 m; 11 Nov. 2019; KOUMAC 2.3 leg.; sable grossier, algues brunes, holothuries; MNHN • 1 specimen, dead; Stn KD551; 20°42.2′ S, 164°18.2′ E; depth 6 m; 10 Nov. 2019; KOUMAC 2.3 leg.; algues brunes; MNHN • 1 specimen, dead; Stn KB625; 20°46.2′ S, 164°22.6′ E; depth 3–4 m; 6 Nov. 2019; KOUMAC 2.3 leg.; fond vaseux à caulerpe, tombant de platier de récif frangeant; MNHN . – Grande Terre, Touho • 8 specimens, dead; Anse de Tiouandé, Stn 1267; 20°43.4′ S, 165°02.0′ E; depth 6–15 m; Sep. 1993; Expédition Montrouzier leg.; sable fin; MNHN • 50+ specimens, living; parages de la Thiem, Stn 1268; 20°45.2′ S, 165°08.0′ E; depth 9–11 m; Sep. 1993; Expédition Montrouzier leg.; sable fin; MNHN • 30+ specimens, living; abords de la Baie de Touho, Stn 1251; 20°46.0′ S, 165°13.0′ E; depth 6–15 m; Sep. 1993; Expédition Montrouzier leg.; vase, sable, herbiers; MNHN • 1 specimen, dead; Banc de Touho, Stn 1259; 20°44.6′ S, 165°13.7′ E; depth 15–35 m; Sep. 1993; Expédition Montrouzier leg.; tombants avec limon; MNHN • 100+ specimens, living; Baie de Touho, Stn 1250; 20°46.7′ S, 165°13.7′ E; depth 3–6 m; Sep. 1993; Expédition Montrouzier leg.; vase sableuse; MNHN • 4 specimens, dead; Baie de Touho, Stn 1237; 20°46.9′ S, 165°13.8′ E; depth 0–1 m; Sep. 1993; Expédition Montrouzier leg.; sable fin et herbiers abrités; MNHN • 14 specimens, dead; Lagon du Grand Récif Mengalia, Stn 1264; 20°44.5′ S, 165°15.9′ E; depth 8 m; Sep. 1993; Expédition Montrouzier leg.; vase sableuse, dôme détritique; MNHN . – Grande Terre, Nouméa • 3 specimens, dead; off Nouville, Stn 1345; 22°16.1′ S, 166°23.7′ E; depth 15 m; 1 Oct. 1992; P. Bouchet leg.; sable grossier sous vase limoneuse, herbiers; MNHN • 40 specimens, living; Anse aux Boeufs, Stn 1500; 22°16.06′ S, 166°25.4′ E; depth 4–6 m; 21 Oct. 2000; Cosel and Trondlé leg.; MNHN • 6 specimens, dead; Baie des Citrons ; 22°18.06′ S, 166°26.07′ E; depth 1–5 m; 17 Feb. 2002; Claude Berthault leg.; MNHN • 2 specimens, dead; Baie des Citrons ; 22°18.06′ S, 166°26.07′ E; depth 1–5 m; 21 Mar. 2002; Claude Berthault leg.; MNHN • 20+ specimens, dead; Baie des Citrons ; 22°17.5′ S, 166°26.2′ E; depth 1–5 m; 1987–2007; Claude Berthault leg.; MNHN • 60+ specimens, living; Anse Vata ; 22°18.1′ S, 166°26.4′ E; depth 1–5 m; 1987–2007; Claude Berthault leg.; MNHN • 1 specimen, dead; Baie de Sainte Marie – Îlot Uéré ; 22°18.5′ S, 166°28.3′ E; depth 0–3 m; 1995-2003; Claude Berthault leg.; MNHN .

Description ( Figs 68 , 71 )

SHELL. Closely resembles that of V. tragema and is of similar size (height up to 3.0 mm). However, in V. semiustus the whorls are more rounded with almost no shoulder (compare Fig. 71A and B ). Additionally, the uppermost spiral cord is of similar size to the other cords ( Fig. 69A ) and the axial pliculae are not as coarse as they are in V. tragema .

COLOUR. In terms of coloration, the shell of V. semiustus , although very variably patterned, is usually considerably more heavily pigmented than that of V. tragema ; commonly with a darker band below the suture and at the periphery, broken up by pale spots; base also often with a spiral band of whitish blotches; some specimens with a paler ground, variously patterned or mottled with darker spots, blotches and axial bands. Interior nacre distinct.

PROTOCONCH ( Fig. 69B ). Typically umboniine, diameter ±170 µm; apical beak present and confluent with terminal lip; apical bulb sculptured with an irregular network of threads, almost hexagonal in places, remainder with distinct subspiral threads; terminal lip weakly convex.

OPERCULUM ( Fig. 69C–D ). Corneous, multispiral, but with rather few whorls and with relatively long growing margin; peripheral fringe broad and with microscopic radial striation; spiral microsculpture distinct.

RADULA ( Fig. 69E–F ). As in V. tragema below.

EXTERNAL ANATOMY (mostly from rehydrated specimens, augmented by photographs of living specimens, Fig. 72A–B ). Head with distinct forehead between cephalic tentacles; snout moderately long, with subterminal papillae; cephalic tentacles long and slender, micropapillate, right and left of similar size; eyestalks long and up-turned, their tips expanded and containing large black eyes; left neck-lobe comprising 4–6 non-papillate, digit-like projections; right neck-lobe well developed, rolled to form exhalant siphon; four micropapillate epipodial tentacles on each side, each with a dark, stalked epipodial sense organ near base; epipodial sense organs could not be discerned beneath neck-lobes; propodium slightly indented in mid-line with a small lateral propodial lobe on each side; foot flattened with broad sole, tapering posteriorly. Head-foot mostly pale translucent white with scattered opaque cream-white pigment spots; forehead and snout with some blackish pigmentation, sometimes also in columellar region above epipodium; cephalic and epipodial tentacles with white transverse bands of spots; epipodial sense organs dark.

Habitat

Mostly associated with muddy substrata, seagrasses and algae, in the inner portions of the lagoon and near estuarine habitats; living specimens at depths of 1–11 m, empty shells washing to 30 m or more in lagoon passes.

Distribution ( Fig. 70 )

Recorded only from New Caledonia (Grande Terre) and Queensland ( Iredale 1929a).

Remarks

Minolia padangensis Thiele, 1925 from the west coast of Sumatra closely resembles V. semiustus , but Thiele considered the latter to have a different colour pattern and somewhat coarser sculpture. Given that V. semiustus exhibits considerable variation in colour and pattern, the significance of these differences needs to be re-evaluated. In any event, Thiele’s species is clearly not referable to Minolia A. Adams, 1860 [ Solariellidae ] and should instead be referred to Vanitrochus .

Another similar species is Cyclostoma (Japonia) musiva Gould, 1859 , a poorly known species thought to be from Japan and currently believed to be a terrestrial species referable to Japonia Gould, 1859 ( Cyclophoridae ) (MolluscaBase 2024). However, although similar, the lectotype of C. musiva at MCZ (Malacology 169253) is twice the size of V. semiustus (height> 6.0 mm). (https://mczbase.mcz.harvard.edu/guid/MCZ:Mala:169253).

Alldredge & King (1977) recorded this species from Lizard Island, Queensland, although their observation that it occurred predominantly in coarse sand in the deep lagoon suggests that the material was in fact V. tragema .

Figures

Fig. 68. Vanitrochus semiustus (Fischer, 1879) (all MNHN). A. Height 2.7 mm, diameter 2.35 mm. B. Height 2.8 mm, diameter 2.35 mm. C. Height 2.9 mm, diameter 2.5 mm. D–F. Height 2.9 mm, diameter 2.7 mm. A, D–F. Ouégoa, environs of Diahot estuary, Stn KD590. B. Koumac, Stn KD557. C. Nouméa, Anse Vata.

Fig. 69. Vanitrochus semiustus (Fischer, 1879) (all MNHN). A. Oblique view of apical whorls. B. Protoconch. C. Operculum. D. Detail of operculum to show microscopic spiral threads. E. Radula half row. F. Radula, oblique view of later-marginal transition. A–B. Koumac, Stn KD557. C–F. Ouégoa, Stn KD590. Scale bars: A= 250 µm; B, D =100 µm; C=200 µm; E= 10 µm; F =20 µm.

Fig. 70. Map of Grande Terre showing the distribution of Vanitrochus semiustus (P. Fisher, 1879) in New Caledonia. Type locality indicated in pink.

Fig. 71. Comparison of shells of New Caledonian Vanitrochus species. A. V. semiustus (Fischer, 1879), Koumac, Stn KD557 (MNHN). B. V. tragema (Melvill & Standen, 1896), Lifou, Stn 1413 (MNHN). Note more rounded whorls of V. semiustus and shouldered whorls of V. tragema with stronger spiral cords. Dimensions of both, height 2.7 mm, diameter 2.3 mm.

Fig. 72. Vanitrochus species, living animals, shell diameter ± 2.3 mm. A. V. semiustus (Fischer, 1879), Koumac [Pandop] marina, Stn KS513 (MNHN-IM-2019-9565) (image PM710). B. V. semiustus, Ouégoa, Diahot estuary, Stn KR981 (MNHN-IM-2019-10140) (image PM832). C–D. V. tragema (Melvill & Standen, 1896), Koumac, Stn KD560 (MNHN-IM-2019-8842) (image PM674).