Parvamussium araneum 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. 8, figs. 3-10]
1991 Parvamussium araneum Dijkstra, 1991
H. H. Dijkstra, 1991, figures 1-10.
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Material.— Holotype, sta. 4.060 NE coast of Sumba, Ε of Melolo, 9°51.8'S 120°46.4Έ, rectangular dredge, depth 240 m, large calcareous stones, small stones, scarce epifauna, 14.ix.1984 (1 live specimen) (RMNH 56531). Paratypes: sta. 4.031 Tukang Besi Islands, Banda Sea, NW of Binongko, 5°54'S 123°58.4'E, Van Veen-grab, depth 300 m, calcareous sand, some shell gravel, 10.ix.1984 (1 specimen + 4 valves, live and dead) (RMNH 56532); sta. 4.153 off SW Salayer, 6°22.4'S 120°26.3Έ, Van Veen-grab, 130-155 m, calcareous sand with some shells and polychaetes, 28.ix.1984 (1 valve) (RMNH 56533).
Description.— Shell small, approximately 9 mm in height and length, convex and circular. Anterior and posterior auricles unequal, umbonal angle about 105°. The external sculpture of the left valve is cancellated by about 25 regular radial costae, increasing in prominence near the ventral margin, and concentric lamellae, which are less conspicuous than the costae. Near the umbonal area only concentric lamellae are present, with microscopic interstitial irregular threads. The concentric squamous lamellae on the anterior auricle are strongly developed, and running over the weakly produced radial costae. The sculpture of the posterior auricle is nearly identical, but there are fewer radial costae.
The exterior surface of the right valve has concentric costae, which are more close set near the umbonal area, with interstitial scratches. The anterior auricle bears about seven tubercular radial costae, which are crossed by concentric costae near the dorsal margin, and scaly on the hinge line. The sculpture of the posterior auricle is more pronounced. Near the umbo the sculpture on the hinge line is smoothed. The interior surface of both valves is provided with three rudimental lirae, and an additional one on the posterior auricle. The cancellated sculpture of the exterior surface of the left valve is easily visible, with small irregular scratches, also of the right valve. The hinge line is straight and the résiliai pit is triangular. The byssal notch is rather small and no ctenolium is developed on the suture. The shell is milky-white and semi-translucent. Dimensions: height 8.9 mm, length 9 mm, diameter 1.3 mm. Etymology.— The surface of the left valve has an appearance of a spider's web. Differentiation.— The most similar congeneric species is Parvamussium vidalense (Barnard, 1964) from off Cape Vidal, Zululand (South Africa), which is different by the following conchological features: less pronounced radial costae on the exterior surface of the left valve, and overrunning concentric lamellae; auricles less sculptured; more internal rudimental lirae; coloration opaque. Remarks.— Barnard (1964: 433) provisionally placed P. vidalense in Cyclopecten, but representatives of this genus have no internal lirae. HENK H. DIJKSTRA, 1991
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«Description. — Shell fragile, up to c. 9 mm high, hyaline to opaque, weakly inflated, circular, auricles unequal, umbonal angle c. 105˚, colour milky-white. Left valve with c. 25 evenly spaced radial costae, increasing in number near ventral margin, crossed by commarginal lamellae, less conspicuous than costae (forming reticulate sculpture), with spines at intersections. Near umbonal area only commarginal lamellae present, with delicate interstitial irregular threads. Identical sculpture on auricles. Right valve sculptured with evenly spaced commarginal lamellae, more close-set near umbonal area, with interstitial scratches. Auricles with irregular reticulate sculpture. Byssal notch narrow. Inner surface of both valves with 3 rudimentary riblets, one additional on posterior auricle. Hinge line straight. Resilifer triangular.
Distribution. — Indonesian Archipelago: 240-300 m (Dijkstra, 1991; Dijkstra & Kastoro (1997); Vanuatu Archipelago: 154-179 m (Dijkstra, 2001); Fiji: 567-699 m, Tonga: 523-806 m, Solomon Islands: 194-286 m (dead) (Dijkstra & Maestrati, 2008). Present material from the Philippines alive in 102-357 m (minimum depth range). The bathymetric range of live-taken specimens is extended to 83-806 m. Remarks. — The present specimens from the Philippines are identical to the type specimens of Parvamussium araneum from Indonesia, although the sculpture of the left valve is somewhat more closely spaced with intercostal commarginal lamellae. This species is a new record for the Philippines.» DIJKSTRA, H. H. 2013. Pectinoidea (Bivalvia: Propeamussiidae and Pectinidae) from the Panglao region, Philippine Islands. Vita Malacologica, 10: 1-108, pls. 1-32, 2 tabs. [p. 17, 18]
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Parvamussium araneum Dijkstra, 1991; H. H. Dijkstra, 2013, Pectinoidea from the Panglao region, Philippine Islands, plate 2, figures 2, 3.
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