Parvamussium virgatum Dijkstra, 1991
DIJKSTRA, H. H. 1991. A contribution to the knowledge of the pectinacean Mollusca (Bivalvia: Propeamussiidae, Entoliidae, Pectinidae) from the Indonesian Archipelago. Zoologische Verhandelingen, 271: 1-57, figs. 1-91. [p. 20, figs. 62-65]
1991 Parvamussium virgatum Dijkstra, 1991
H. H. Dijkstra, 1991, figures 53-64
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Material.— Holotype, sta. 4.033 Tukang Besi Islands, Banda Sea, NW of Binongko, 5052.5'S 123°58.5Έ, Van Veen-grab (2x), depth 250-290 m, coarse calcareous sand, 10.ix.1984 (left valve) (RMNH 56556); Paratypes, sta. 4.033 (2 valves) (RMNH 56557); sta. 4.019 Tukang Besi Islands, Banda Sea, S of Kaledupa reef, 5°57.5'S 123°46.5Έ, Van Veen-grab (2x), depth 285-305 m, shell gravel and foraminifera sand, 9.ix.1984 (1 valve) (RMNH 56558); sta. 4.034 Tukang Besi Islands, Banda Sea, NW of Binongko, 5°525'S 123°58.5Έ, Van Veen-grab, depth 280 m, coarse calcareous sand, 10.ix.1984 (1 valve) (RMNH 56559).
Description.— Shell small, convex and subcircular, approximately 10 mm both in height and length. Anterior and posterior auricles unequal, umbonal angle about 110°.
The white exterior surface, down to 2 mm beneath the umbo, is smooth and glossy, with microscopic scratches and growth-lines. The central part of the shell-disc is dull dirty white and provided with some irregular very fine radial lines, which are more coarse near the posterior margin. Near the ventral margin microscopic concentric lamellae are present. The anterior and posterior auricles also bear very fine concentric lamellae, which are most prominent near the dorsal margin. The white, opaque and glossy interior surface has ten lirae, which are developed to nearly 3 mm from the ventral margin. A small lira is visible on each border of the auricles. The hinge line is straight. The cardinal crura is rather broad and the résilial pit triangular. Dimensions: height and length 10.5 mm. Etymology.— The exterior surface of the holotype is irregularly fine radially striped. Differentiation.— The most closely related species is Parvamussium formosum (Melvill in Melvill & Standen, 1907) from the Gulf of Oman. P. formosum differs from P. virgatum by (1) the more prominent irregular radial lines near the anterior and posterior margins, (2) the auricles, that are more clearly radiated with very small costae, (3) microscopic lamellae near the ventral margin, (4) the presence of some rudimental lirae, (5) the absence of the smaller cardinal crura and (6) the semitransparent shell. Remarks.— Unfortunately no live material is found and right valves could not be traced with certainty. Juveniles cannot be distinguished with certainty from P. scitulum.» HENK H. DIJKSTRA, 1991
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