Vanitrochus tragema ( Melvill & Standen, 1896 )

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 : 128-133

Vanitrochus tragema ( Melvill & Standen, 1896)

Figs 71B , 72B , 73–76

Solariella (Conotrochus) tragema Melvill & Standen, 1896: 313 , pl. 11 fig. 78. Type locality: Lifou, Loyalty Islands, New Caledonia (Hadfield).

Monilea tragema – Hedley 1899: 405.

Vanitrochus tragema – Iredale 1929a: 272, 295. — Herbert 1989: 371, fig. 1g (lectotype), fig. 4d–f. — Wilson 1993: 95, text fig. — Héros et al. 2007: 210.

Vanitrochus cf. tragema – Poppe et al. 2006: 114, pl. 71 fig. 3.

Material examined

Lectotype (designated by Herbert 1989) ( Fig. 73D ) NEW CALEDONIA • Loyalty Islands, Lifou; Hadfield leg.; NMW.1955.158.01503 .

Paralectotypes NEW CALEDONIA • 1 specimen; Loyalty Islands, Lifou; Hadfield leg.; NMW.1955.158.00148 • 2 specimens; Loyalty Islands, Lifou; Hadfield leg.; MM.EE.3792 and MM.EE.7908 .

Other material

NEW CALEDONIA – Grande Terre, Koumac • 2 specimens, living; Stn KD532; 20°31.3′ S, 164°04′ E; depth 12–13 m; 5 Nov. 2019; KOUMAC 2.3 leg.; sable blanc nu; DNA vouchers; MNHN--IM-2019-7646 and -7647 • 4 specimens, dead; Stn KD533; 20°32.2′ S, 164°05.5′ E; depth 11 m; 5 Nov. 2019; KOUMAC 2.3 leg.; sable blanc nu; MNHN • 7 specimens, living; Stn KD563; 20°33.4′ S, 164°06.3′ E; depth 5 m; 15 Nov. 2019; KOUMAC 2.3 leg.; sable blanc; MNHN • 1 specimen, living; Stn KD534; 20°32.4′ S, 164°07.2′ E; depth 16 m; 5 Nov. 2019; KOUMAC 2.3 leg.; sable blanc, éponges, Halophila , algues brunes, Halimeda ; MNHN • 1 specimen, dead; Stn KB608; 20°34.9′ S, 164°07.6′ E; depth 15 m; 31 Oct. 2019; KOUMAC 2.3 leg.; patch coralliens sur sable d’arrière terrasse de récif barrière; MNHN • 13 specimens, dead; Chenal de l’Infernet, Stn 1306; 20°39.1′ S, 164°12.4′ E; depth 11–13 m; Oct. 1993; Expédition Montrouzier leg.; fonds blancs; MNHN • 1 specimen, dead; Chenal de l’Infernet, Stn 1304; 20°38.6′ S, 164°13.2′ E; depth 12–15 m; Oct. 1993; Expédition Montrouzier leg.; sable gris, dalle; MNHN • 1 specimen, dead; Stn KD541; 20°39′ S, 164°13.3′ E; depth 11 m; 7 Nov. 2019; KOUMAC 2.3 leg.; sables gris; MNHN • 2 specimens, dead; Récif de l’Infernet, Stn KB600; 20°36.6′ S, 164°14.4′ E; depth 1 m; 28 Oct. 2019; KOUMAC 2.3 leg.; corail mort, corail vivant, débris de tombant interne de massif corallien intermédiaire, corail mort, débris, qq coraux vivants de platier de massif corallien intermédiaire; MNHN • 1 specimen, dead; Passe Deverd, Stn 1321; 20°44.7′ S, 164°14.9′ E; depth 90–115 m; Oct. 1993; Expédition Montrouzier leg.; sable vaseux; MNHN • 3 specimens, living; Stn KD560; 20°45.6′ S, 164°15.2′ E; depth 5–9 m; 14 Nov. 2019; KOUMAC 2.3 leg.; sable blanc et quelques algues brunes; DNA voucher, photographed alive (image PM674); MNHN-IM-2019-8842 • 3 specimens, dead; Stn KD552; 20°49.4′ S, 164°18.5′ E; depth 10–11 m; 13 Nov. 2019; KOUMAC 2.3 leg.; sable blanc; MNHN. – Grande Terre, Touho • 1 specimen, dead; Lagon du Grand Récif Mengalia , Stn 1266; 20°39.6′ S, 165°14.7′ E; depth 10–15 m; Sep. 1993; Expédition Montrouzier leg.; paté corallien; MNHN • 40+ 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 • 4 specimens, dead; Lagon du Grand Récif Mengalia , Stn 1263; 20°45.0′ S, 165°16.0′ E; depth 6 m; Sep. 1993; Expédition Montrouzier leg.; sable vaseux avec patés coralliens; MNHN. – Grande Terre, Nouméa • 5 specimens, dead; Récif Senez , Stn 1350; 22°17.9′ S, 166°19.6′ E; depth 369 m; 23 Nov. 1992; Bouchet and Marshall leg.; pente interne; MNHN. – Loyalty Islands, Lifou • 8 specimens, dead; Baie du Santal, north of Cap Aimé Martin [=Acadro], Stn 1450; 20°45.8′ S, 167°01.6′ E; depth 27–31 m; 17 Nov. 2000; Atelier LIFOU 2000 leg.; brossages; MNHN • 1 specimen, dead; Baie du Santal , north of Cap Aimé Martin [= Acadro], Stn 1449; 20°45.8′ S, 167°01.6′ E; depth 17 m; 17 Nov. 2000; Atelier LIFOU 2000 leg.; brossages; MNHN • 2 specimens, living; Baie du Santal , Baie de Gaatcha , towards Cap Mandé , Stn 1424; 20°54.9′ S, 167°03.0′ E; depth 4 m; 15 Nov. 2000; Atelier LIFOU 2000 leg.; sable fin et algues photophiles sur dalle; MNHN • 1 specimen, dead; Baie du Santal , entre le Cap Wekutr et le Cap Wajez , Stn 1410; 20°56.7′ S, 167°03.1′ E; depth 2–4 m; 25 Nov. 2000; Atelier LIFOU 2000 leg.; bord du platier; MNHN • 9 specimens, dead; Baie du Santal , Baie de Gaatcha , Stn 1436; 20°55.5′ S, 167°04.2′ E; depth 20 m; 10 Nov. 2000; Atelier LIFOU 2000 leg.; patate corallienne sur tombant; MNHN • 1 specimen, dead; Baie du Santal , Baie de Gaatcha , Stn 1419; 20°55.6′ S, 167°04.5′ E; depth 5 m; 10 Nov. 2000; Atelier LIFOU 2000; limon sur dalle, algues photophiles; MNHN • 100+ specimens, living; Baie du Santal , in front of landing beaches at Drueulu , Stn 1413; 20°55.3′ S, 167°05.0′ E; depth 3–10 m; 26 Nov. 2000; Atelier LIFOU 2000 leg.; fonds meubles; MNHN • 4 specimens, dead; Baie du Santal , W/SW of Pointe d’Easo , Stn 1430; 20°47.5′ S, 167°07.1′ E; depth 20–25 m; 9 Nov. 2000; Atelier LIFOU 2000 leg.; patates coralliennes, passées séd.; MNHN • 1 specimen, dead; Baie du Santal , Baie d’Huneté , Stn 1425; 20°46.8′ S, 167°07.2′ E; depth 4–5 m; 17 Nov. 2000; Atelier LIFOU 2000 leg.; dalle avec couverture sed.; MNHN • 8 specimens, dead; Baie du Santal , off Peng , Stn 1423; 20°54′ S, 167°07.3′ E; depth 12 m; 14 Nov. 2000; Atelier LIFOU 2000 leg.; passées sableuses entre patates; MNHN • 4 specimens, dead; Baie du Santal , off Peng , Stn 1412; 20°54.2′ S, 167°07.4′ E; depth 2–5 m; 14 Nov. 2000; Atelier LIFOU 2000 leg.; fonds meubles; MNHN • 6 specimens, living; Baie du Santal , in front of Chépénéhé , Stn 1415; 20°47.1′ S, 167°09.1′ E; depth 3–7 m; 25 Nov. 2000; Atelier LIFOU 2000 leg.; sable; MNHN • 8 specimens, living; Baie du Santal , Pointe de Chépénéhé , Stn 1420; 20°47.7′ S, 167°09.4′ E; depth 4–5 m; 18 Nov. 2000; Atelier LIFOU 2000 leg.; dalle avec couverture séd.; MNHN • 1 specimen, living; Baie du Santal , in front of Kiki , Stn 1411; 20°47.6′ S, 167°10.4′ E; depth 48 m; 23 Nov. 2000; Atelier LIFOU 2000 leg.; sable entre patates; MNHN .

Description ( Figs 71 , 73 )

SHELL. Resembles that of Vanitrochus semiustus and is of similar size (height up to 3.0 mm). Differs in that whorls are distinctly shouldered, with spiral cord delineating shoulder stronger than other cords ( Fig. 71B ). Axial sculpture on apical whorls also stronger, resulting in coarser beading on spiral cords ( Fig. 74A ).

COLOUR. Colouration highly variable; pattern rarely as dark as that of V. semiustus ; commonly whitish with blotches on shoulder in shades of brown, olive-green or pinkish-red; smaller spots at periphery, and base with broad, mottled subperipheral band with rays radiating inward toward but not into umbilicus. Occasional specimens uniformly whitish ( Fig. 73E ), others with flecks of pigment on spiral cords ( Fig. 73H ) or almost bicoloured ( Fig. 73J ). Interior nacreous, but less distinctly so than in V. semiustus .

PROTOCONCH ( Fig. 74B ). Typically umboniine, diameter 160–170 µm; apical beak present, 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. 74C–D ). Corneous, multispiral, but outer whorls relatively broad and with long growing margin; peripheral fringe broad, with well-developed radial striation; spiral microsculpture distinct.

RADULA ( Fig. 75 ). Formula ∞+(1)+ 5+1+ 5+(1) +∞, with 20–25 transverse rows of teeth; teeth of central field reduced; rachidian base-plate rounded, with indistinct vestige of shaft at centre of anterior edge; base-plates of lateral teeth thin, extensively overlapping, outer edge rounded and raised anteriorly, leading to narrow shaft vestige. First marginal tooth transitional, lacking shaft and cusp ( Fig. 75C arrow), its base-plate arched and with a longitudinal medial hollow to accommodate shaft of outer neighbour. Subsequent inner marginal teeth well developed with a narrow shaft and strongly recurved cusp; cusp deeply divided into five (usually) lanceolate denticles, middle one largest; cusps of marginal teeth progressively smaller toward edge of radula and with more slender, more numerous denticles; outermost marginals with finely pectinate margins.

EXTERNAL ANATOMY ( Fig. 72C–D ). As for V. semiustus above. Photograph of living animal showing purple pigmentation on snout.

Habitat

Mostly associated with white, sandy substrata toward the outer portions of the lagoon; living specimens at depths of 4–16 m, exceptionally to 48 m, empty shells washing to 90 m or more in lagoon passes.

Distribution ( Fig. 76 )

Described from the Loyalty Islands, with additional rather sparse records from Grande Terre (perhaps often overlooked). Recorded also from Tuvalu ( Hedley 1899), and Queensland ( Iredale 1929a; Wilson 1993). A tentatively identified specimen from the Philippines ( Poppe et al. 2006) also appears correct.

Remarks

Vanitrochus geertsi Poppe, Tagaro & Dekker, 2006 from the Philippines has fewer, coarser spiral cords and appears very similar to Monilea (Minolia) singaporensis Pilsbry, 1889 , with which it merits closer comparison. Hedley’s record of a specimen of V. tragema from Tuvalu with a height of 4.5 mm ( Hedley 1899) is exceptional and requires confirmation.

Figures

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).

Fig. 73. Vanitrochus tragema (Melvill & Standen, 1896). A–C. Koumac, Stn KD563, height 2.5 mm, diameter 2.3 mm (MNHN). D. Lectotype of Solariella (Conotrochus) tragema Melvill, & Standen, 1896, Lifou, height 2.5 mm, diameter 3.1 mm (NMW.1955.158.01503). E. Koumac, Stn KD534, height 2.3 mm, diameter 2.0 mm (MNHN). F. Lifou, Stn 1420, height 2.35 mm, diameter 2.05 mm (MNHN). G. Lifou, Stn 1413, height 2.55 mm, diameter 2.1 mm (MNHN). H–I. Lifou, Stn 1413, height 2.8 mm, diameter 2.35 mm (MNHN). J. Lifou, Stn 1413, height 2.85 mm, diameter 2.43 mm (MNHN).

Fig. 74. Vanitrochus tragema (Melvill & Standen, 1896) (all MNHN). A. Oblique view of apical whorls. B. Protoconch.C. Operculum. D. Detail of operculum to show microscopic spiral threads.A–B. Koumac, Stn KD563. C–D. Lifou, Stn 1424. Scale bars: A, C =250 µm; B=50 µm; D =100 µm.

Fig. 75. Vanitrochus tragema (Melvill & Standen, 1896), radula, Koumac, Stn KD563 (all MNHN). A. Full width of radula. B. Half width of radula. C. Oblique view of lateral to inner marginal transition, lateral teeth numbered 1–5, transitional innermost marginal arrowed. D. Oblique view of marginal teeth. Scale bars: A= 25 µm; B =20 µm; C–D =10 µm.

Fig. 76. Map showing the distribution of Vanitrochus tragema (Melvill & Standen, 1896) in New Caledonia. Type locality (approximate) indicated in pink.