Propeamussium caducum (E. A. Smith, 1885)
SMITH, E. A. 1885. Report on the Lamellibranchiata collected by H.M.S. Challenger during the years 1873-76. In C. W. Thomson & J. Murray: Report on the Scientific Results of the Voyage of H.M.S. Challenger during the years 1873-1876. Zoology, 13: 1-341, pls. 1-25 [p. 309, pl. 23, figs. 1-1c]
1885 Amussium [sic] caducum E. A. Smith, 1885
1911 Amusium electrum Pelseneer, 1911
1912 Amusium weberi Dautzenberg & Bavay, 1912
1932 Propeamussium nakazawai Kuroda, 1932
1911 Amusium electrum Pelseneer, 1911
1912 Amusium weberi Dautzenberg & Bavay, 1912
1932 Propeamussium nakazawai Kuroda, 1932
E. A. Smith, 1885, plate 23.
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«Testa tenuissima, pellucida, rotundata, compressa, superne angustata, producta, paulo inaequivalvis (valva dextra sinistra leviter convexiore) utrinque conspicue hians. Valva dextra polita, concentrice exilissime striata, striisque radiantibus obsoletis sculpta; sinistra nitida, concentrice minuta lamellata, minutissimeque radiatim striata. Auriculae minimae, subaequales. Pagina interna nitida, liris albis tenuibus denis instructa.
This species is rather higher than hmg, romuloil, Imt narrowed and produced above. It is very thin, slightly inequivalve, gaping considerably on both sides, glossy, pellucid around the outer margin, and rather thicker and more opaque towards the beaks. The right valve is the deeper, somewhat more shining than the left, exhibiting very fine lines of growth and indistinct radiating substriations. The left valve is more strongly concentrically sculptured, and the radiating striae are more dense and stronger. The auricles are very small and almost of the same size. The beaks are acute, forming an apical angle of about 105 degrees, the converging dorsal lines being slightly concave. The interior of the valves towards the umbones, and rather more than half way across the valves, is more opaque than exteriorly, and is strengthened by ten white slender lirae of different lengths. The outer pellucid zone of the right valve is very prettily blue-prismatic within.
Length 20 mm., height 22, diameter 4½. Habitat.— Station 207, west of the island of Luzon, Philippines, at a depth of 700 fathoms; blue mud. The chief characteristics of this species besides form, are its fragility, fine sculpture, glossy surface, and the ten radiating costellae. The right valve is somewhat yellowish, and the left whiter.» EDGAR ALBERT SMITH, 1885
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«Description. — Shell fragile, glossy, transparent or opaque, up to c. 25 mm high, inequivalve, equilateral, somewhat higher than wide, left valve slightly more convex than right, with lateral gape, umbonal angle c. 90˚, prodissoconch c. 215 μm in height (Knudsen, 1967). Cream or brownish, right valve somewhat brighter than left.
Left valve smooth, with commarginal growth lines, no radial striations. Auricles small, also smooth, somewhat raised near margins. Right valve with wide-set commarginal lirae, commencing at 3 mm shell height and extending to submarginal area, with interstitial microscopic radial scratches. Auricles with very delicate commarginal striae, prominent scales produced on marginal areas of hinge. Hinge line straight near umbo, then rising near anterior and posterior dorsal margins. Internal riblets 10 in number in most specimens, 9 or 11 in a few, slightly nodulose at distal ends. Riblets of right valve somewhat more prominent than in left valve. No byssal notch. Distribution. — Gulf of Aden: 1295 m, Zanzibar area: 786 m, Arabian Sea and Bay of Bengal: 691-1483 m, Japanese waters: c. 200 m and Philippine Islands: 548-1500 m (Knudsen, 1967); Indonesian Archipelago: 452-840 m (Knudsen, 1967; Dijkstra, 1991; Dijkstra & Kastoro, 1997); New Caledonia: 450-960 m (Dijkstra (1995b, 2001); Vanuatu Archipelago: 602-650 m (Dijkstra, 2001); Solomon: 367-696 m (Dijkstra & Maestrati, 2008). Present material from the Philippines alive in 200-923 m (minumum depth range). The bathymetric range of live-taken specimens is now 90-1500 m. Remarks. — Pelseneer (1911) only described and figured the soft parts of A. electrum, which he had used for his comprehensive anatomical study, but not the valves. These valves and soft parts have not been recovered in the KBIN. The specific epithet is probably reduced from Bavay’s manuscript name "Amussium electricum" [KBIN], which he later changed to Amussium weberi. However, as the anatomy was described by Pelseneer (1911), A. electrum is an available name, a further synonym of A. caducum. Amussium weberi is morphologically similar to A. caducum, although in typical material the colouration (A. caducum hyaline and whitish, A. weberi hyaline and creamy) and internal ribs (A. caducum eight, A. weberi seven) are slightly different. However, intermediate variations are also observed (MNHN, ZMA).
All morphological characters of the present material are identical to the type specimens.» 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. 11]
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Propeamussium caducum (E.A. Smith, 1885); H. H. Dijkstra, 2013, Pectinoidea from the Panglao region, Philippine Islands, plate 1, figures 1a-1d.
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