Parvamussium perspicuum, Dijkstra & Maestrati, 2013

Dijkstra, Henk H. & Maestrati, Philippe, 2013, New species and new records of bathyal living Pectinoidea (Bivalvia: Propeamussiidae: Pectinidae) from the Southwest Pacific, Zoosystema 35 (4), pp. 469-478 : 472

Parvamussium perspicuum n. sp. ( Fig. 2 A-H)

TYPE MATERIAL. — Vanuatu. BOA 1, stn CP 2480, 16°44’S, 167°49’E, 632-677 m, holotype spm ( MNHN 25747). — Same data, paratype spm ( MNHN 25748).

TYPE LOCALITY. — Vanuatu Archipelago, SE Malekula, Banc de Chauliac, 16°44’S, 167°49’E, 632-677 m ( BOA 1, stn CP 2480).

ETYMOLOGY. — Shell disc translucent (Latin perspicuus, adjective meaning translucent).

DISTRIBUTION. — Vanuatu Archipelago, live in 632- 677 m depth.

DESCRIPTION

Shell up to c. 4 mm in height, fragile, nearly circular, weakly inflated, left valve more convex than right valve, inequivalve, almost equilateral, anterior auricle slightly larger than posterior, left valve more translucent than right valve.

Left valve disc smooth and hyaline. Anterior auricle with a few growth lines laterally, posterior auricle opaque whitish with weak, delicate, closely spaced commarginal sculpture laterally.

Right valve disc semi-translucent with commarginal lirae, closely spaced in early growth stage, wider in adult stage. Auricles with commarginal growth lines, hinge scaly antero-dorsally on anterior auricle. Byssal notch moderately deep,byssal fasciole narrow.Internal ribs 8, commencing 1.5 mm from the top margin towards 1 mm from the ventral margin, small in early growth stage to prominent broad in adult stage.

Dimensions of holotype: H 4.2 mm, W 4.2 mm, D 1.0 mm.

REMARKS

Parvamussium perspicuum n. sp. and Parvamussium torresi ( Smith, 1885) , known from the bathyal southwestern Pacific, have both a smooth left valve disc, but other characters differ, i.e. in size ( P. perspicuum n. sp. up to 4 mm, P. torresi up to 12 mm in height), in transparency ( P.perspicuum n. sp. left valve glossy and hyaline, P. torresi semi-translucent or opaque whitish), in sculpture ( P.perspicuum n. sp. has a completely smooth left valve disc, P. torresi has delicate closely spaced commarginal lamellae near the ventral margin), and in number of internal ribs ( P. perspicuum n. sp. 8, P. torresi 10-12 with one or two interstitial rudimentary riblets).

Figures

FIG. 2. — Parvamussium perspicuum n. sp.:A, B, E, F, holotype MNHN 25747;A, external view of the left valve;B, external view of the right valve; E, detail of the commarginal striae of the external side of the right valve; F, idem, detail inter striae; C, D, G, H, paratype MNHN 25748;C, internal view of the left valve; D, internal view of the right valve;G, Prodissoconch of the right valve;H, prodissoconch of the left valve. Scale bars: A-D, 1 mm; E, 100 µm; F, 20 µm; G, H, 50 µm.