Parvamussium vesiculosum, Dijkstra & Maestrati, 2013

Dijkstra, Henk H. & Maestrati, Philippe, 2013, Pectinoidea (Bivalvia: Propeamussiidae, Entoliidae and Pectinidae) from the Tarava Seamounts, Society Islands and the Tuamotu Archipelago (French Polynesia), Zoosystema 35 (3), pp. 361-375 : 367-368

Parvamussium vesiculosum n. sp.

(Fig. 3)

TYPE MATERIAL. — Tarava Seamounts. Tarasoc, stn DW 3310, 19˚13’S, 151˚37’W, 613-698 m, holotype lv ( MNHN 25704 ) ; stn DW 3328, 18˚46’S, 152˚15’W, 788-836 m, paratype lv ( ZMA Moll. 398324) .

TYPE LOCALITY. — Tarava Seamounts, Mont Ari’i Moana, 19˚13’S, 151˚37’W, 613-698 m (Tarasoc, stn DW 3310).

ETYMOLOGY. — Left valve covered with blisters (latin: vesiculosus, adjective meaning vesiculose).

OTHER MATERIAL EXAMINED. — Society Islands. Tarasoc, stn DW 3408, 16˚25’S, 152˚17’W, 437-536 m, 1 lv.

DISTRIBUTION. — Tarava Seamounts and Society Islands, only single valves at 437-836 m depth.

DESCRIPTION

Shell up to c. 12 mm high, circular, almost equilateral, weakly inflated, anterior auricle somewhat larger than posterior, opaque whitish. Prodissoconch 230 µm long.

Left valve disc smooth, glossy and transparent in early growth stage to c. 2 mm from dorsal margin, followed by c. 10 radial rows of distant vesicles (c. 4 per mm) increasing in number by intercalated radial rows of vesicles to c. 40 near ventral margin. Commarginal sculpture on disc lacking. Anterior auricle sculptured with prominent, closely spaced, commarginal lamellae (c. 8 per mm), posterior auricle almost identically sculptured with slightly more closely spaced and less prominent commarginal lamellae (c. 10 per mm). Hinge line straight. Internal riblets (12 and one auricular on each side) commence in late growth stage on central part of inner surface and extend to ventral submarginal area.

Dimensions of the holotype: H 12.1 mm, W 12.0 mm.

REMARKS

Although only single left valves are present of Parvamussium vesiculosum n. sp., this species can be distinguished from other congeners easily by its conspicuous vesicular sculpture.

The present species is morphologically closest to Parvamussium vesiculatum Dijkstra, 1995 , known from the southwestern Pacific ( Dijkstra & Maestrati 2008: 96), but differs in size ( P. vesiculosum n. sp. up to 12 mm high, P.vesiculatum up to 6 mm), in having more radial rows and intercalated secondary radial rows of vesicles on the left valve ( P. vesiculatum has fewer radial rows of vesicles and in addition, vesicles are present on intersections with the commarginal lamellae [see Dijkstra& Maestrati 2008:figs 93, 94]), in having a smooth,glossy and transparent early growth stage ( P.vesiculatum with widely spaced commarginal sculpture [see Dijkstra & Maestrati 2008: fig. 96]), and in having more prominently developed internal ribs ( P.vesiculatum only a few rudimentary laterally).

The specimen of P. vesiculosum n. sp. from the Society Islands is slightly different from the type material in having fewer and coarser radial vesicles.