Parvamussium propinquum (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. 314, pl. 23, figs. 7-7b]
1885 Amussium [sic] propinquum E. A. Smith, 1885
1897 Amussium [sic] sublucidum Dautzenberg & Fischer, 1897
1897 Amussium [sic] sublucidum Dautzenberg & Fischer, 1897
E. A. Smith, 1885, plate 23.
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«Testa valde compressa, tenuissima, pellucida, nitida, rotundata; valva dextra laevis, incrementi lineis parum conspicuis sculpta, sinistra radiatim tenuiter lirata. Auriculae subaequales, lateribus concavis. Pagina interna nitida, liris capilliformibus duodenis instructa.
This species, of which only two odd valves are at present known, is very fragile, pellucid, much flattened, glossy, and about ecjuilateral. It is of a rounded form, perhaps a trifle longer than high, and has rather a long hinge-line. The auricles are small, not quite equal, those of the right valve (the only one perfect at this part) being decidedly concave at the sides, and sculptured with fine lines of growth. The umbones are small, project a trifle beyond the straight hinge-margin, and have the sides very faintly concave and converging to an apical angle of about 125 degrees. The right valve is smooth, exhibiting only very fine lines of increase, which, however, are rather more visible near the outer margin than elsewhere. The left valve, besides these concentric striae, is sculptured with numerous fine radiating lirae. The interior of the valves is glossy, and strengthened with twelve excessively fine hair-like lirae, which attain neither to the umbones nor to the circumference. The shorter ones beneath the ears are the thickest. The left valve appears radiately striated within, each stria corresponding with an external lira. The ligamental pit is very minute.
Length 7½ mm., height 6⅔. Habitat.— Station 78, east of the Azores, at a depth of 1000 fathoms; volcanic mud. This species, although bearing a general resemblance to Amussium lucidum, differs (judging from the only two valves known) in being proportionally shorter from the beaks to the ventral outline, in comparison with the transverse diameter. Its hinge-line is longer, the apical angle of the beaks less acute, the left valve is radiately lirate instead of concentrically striate, the anterior ear in the same valve is quite distinct in form, and the internal lirae are more slender and fewer than in the Azorean examples of Amussium lucidum.» EDGAR ALBERT SMITH, 1885
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«Type locality
The Azores, 1829 m depth. Distribution
Tropical to temperate eastern Atlantic (ca. 40°N-20°N), now extended to Iceland (ca. 65°N) with a depth range from 790 m (Dijkstra & Goud 2002) to 4060 m (Locard 1898). BIOICE material alive at 6 stations in 1295-2007 m (Map 2). Description
Shell (Figures 1I,J, 3A-3D) up to ca. 7 mm high, fragile, transparent to opaque, nearly circular, somewhat longer than high, slightly drawn out posteroventrally, left valve slightly more convex than right valve; auricles small, nearly equal in size, umbonal angle ca. 125°. Prodissoconch (Figures 2E), length ca. 200 μm, colour whitish. Left valve (Figures 4G, 8C) smooth at central part of disc with fine closely spaced, radial riblets and commarginal lamellae near the margin. Right valve (Figures 4H, 8D) sculptured with regularly arranged commarginal lirae. Hinge line rather long and straight and very weakly sculptured with close-set lamellae. Inside of valve usually with 12 short and narrow radial riblets, sometimes with several rudimentary interstitial ones. Ribs commence near the central part and extend to the submarginal area. Byssal notch well-developed, ctenolium lacking. Remarks
The Icelandic specimens have a somewhat weaker sculpture than the type material and usually lack the radial sculpture on the left valve. Adult specimens from the Azores often have smaller, intercalated, internal riblets, which are not present in Icelandic specimens. Parvamussium propinquum differs from Propeamussium lucidum in having a circular circumference (P. lucidum is generally higher than long), larger anterior auricles, a well-developed byssus notch (in P. lucidum, weak and shallow), and in having more numerous internal ribs (in P. propinquum 12, with several rudimentary ones commencing when halfgrown; in P. lucidum usually only 9, developing early).» DIJKSTRA, H. H., A. WARÉN & G. GUDMUNDSSON. 2009. Pectinoidea (Mollusca: Bivalvia) from Iceland. Marine Biology Research, 5: 207-243, figs. 1-20. [p. 214]
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Parvamussium propinquum (Smith, 1885); H. H. Dijkstra, A. Warén & G. Gudmundsson, 2009, Pectinoidea (Mollusca: Bivalvia) from Iceland, figures 1I, 1J, 3A-3D.
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