Propeamussium siratama (Oyama in Kuroda, 1951)
OYAMA, K. 1951. Amusiinae in Japan. In: T. Kuroda (ed.), 1949-1953, Illustrated Catalogue of Japanese Shells, 216 p., 13: 79-86, pl. 13, text-figs. 1-4. [p. 80, pl. 13, figs. 5-7]
1951 Ctenamussium (Micramussium) siratama Oyama in Kuroda, 1951
T. Oyama, 1951, plate 13.
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«Shell small, thin, rather circular, almost equilateral and nearly equivalves. Auricles cornparatively small, subtriangular, but antero- and postero-dorsal corners are fairiy rounded; hinge margins of the auricles straight and crenulated. Surface almost smooth, but the detailed sculpture of the two valves is microscopically different. The left valve having numerous fine radial striations, which are more or less distinct near the umbo, especially on the auricles they are more distinct. Internal lirae ten in number, both outermost ones situating on the base of the auricles; other lirae are somewhat stronger and with rounded ends; each lirae begining from the beak cavity reaching close to the ventral margin. The left valve being pellucid white; the right fawn-colour; and the both valves showing through the internal lirae as white lines. Inside of both valves with brilliantly vitreous gloss.
Length 7.5 mm., height 7.4 mm., breadth 2.8 mm. (figured type specimen). Type locality: Off Manazuruzaki, Sagami Sea, (159—128 fms.)» KATURA OYAMA, 1951
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«Type data. — Holotype (H 7.4 mm, pv), the type material is possible in the Toba Aquarium at Toba, Japan, but Oyama (pers. comm.) could not trace it. Type locality: Japan, Sagami Sea, off Manazuruzaki, 159-128 fathoms [= 291-234 m], alive.
Description. — Shell fragile, up to c. 19 mm high, generally smaller up to c. 12 mm in height, circular, nearly equivalve, equilateral, slightly inflated, auricles equal in shape and size, umbonal angle 110-115˚. Prodissoconch c. 200 μm in height. Colour whitish or pale-brown transparent. Left valve sculptured with delicate, irregularly spaced radial lirae from early growth stage until beyond central part of disc, with microscopic regularly spaced commarginal lamellae, smooth central part and periphery. Auricles frequently smooth, sometimes with fine commarginal lirae. Right valve sculptured with delicate, regularly spaced commarginal lirae, more prominent near ventral margin. Inner surface with 9-10 ribs, sometimes with a rudimentary intercostal riblet. Hine line straight. No byssal fasciole, or byssal notch. Ctenolium lacking. Distribution. — Japan: 100-300 m (Hayami, 2000: 913), Taiwan: 310-440 m (Dijkstra & Maestrati, 2009: 39); Indonesia: 283-285 m (Dijkstra & Kastoro, 1997: 253), Solomons and Fiji: 273-1004 m (Dijkstra & Maestrati, 2008: 85); New Caledonia: 316-533 m (Dijkstra, 2001: 82). Present material from the Philippines alive in 400-602 m (minimum depth range). The bathymetric range of live-taken specimens is 100-1004 m. Remarks. — The present specimens from the Philippines fit the original description (type material untraceable) and studied material from Japan (ZMA, NSMT), but differ in having fewer internal ribs (7 + 2 auricular, typical 8 + 2 auriclar), and in colour (left valve orange, typical whitish). Other morphological characters are identical. 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. 15, 17]
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Propeamussium siratama (Oyama, 1951); H. H. Dijkstra, 2013, Pectinoidea from the Panglao region, Philippine Islands, plate 2, figures 1a-1d.
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