Propeamussium arabicum Dijkstra & Janssen, 2013
DIJKSTRA, H. H. & A. W. JANSSEN. 2013. Bathyal and abyssal Pectinoidea from the Red Sea and Gulf of Aden (Bivalvia: Propeamussiidae, Entoliidae, Pectinidae). Archiv für Molluskenkunde, 142 (2): 181-214, figs. 1-57. [p. 184, figs. 1, 2, 7-9]
2013 Propeamussium arabicum Dijkstra & Janssen, 2013
H. H. Dijkstra & A. W. Janssen, 2013, figures 1-3, 4-12.
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«Material examined: Gulf of Aden: ‘Meteor 31’, stn 105.3, 5 v (SMF); Stn 105.4, 287 v (SMF), 14 v (MBUR), 40 v (RMNH); Stn 105.5, 62 v (SMF), 11 v (RMNH).
‘Meteor 5’, stn 250, 1 v (SMF); Stn 267, 5 v (SMF); Stn 286, 30 v (SMF). Type material: Holotype (lv) SMF 341743; 108 paratypes (v): MBUR (14 v), RMNH MOL.329826 (40 v), SMF (SMF 341744-341747, 341748/50, ). The additional valves of the type and other stations are not belonging to the type series. Type locality: ‘Meteor 31’, stn 105.4, Gulf of Aden, 12°21.5'N, 44°33.0'E, 506 m, grey-greenish sandy mud, 04.III.1995. Description: Shell small, up to 14.9 mm high, fragile, transparent, somewhat higher than wide, inequivalve, equilateral, left valve slightly more convex than right valve, auricles slightly unequal, umbonal angle 110–115°, colour of left valve creamy, right valve whitish. Left valve sculptured (fig 1a–c) with numerous delicate, regularly spaced, antimarginal lirae, crossed by irregularly arranged, minutely undulated growth lines, commencing 1 mm below umbo and extending to above central part of disc, central part and periphery smooth. Anterior auricle somewhat larger than posterior with fine commarginal lirae, weaker on posterior. Dorsal margin weakly lamellated near anterior margin. Right valve sculptured with fine, regularly close-set commarginal lirae, more widely spaced near ventral margin. Auricles smooth, unequal in form and size. No byssal fasciole or byssal notch. Ctenolium absent. Hinge line straight. Interior ribs of both valves prominent (7 with 2 auricular ones) commencing in early growth stage and extending to submarginal area. No rudimentary interstitial riblets.
Dimensions of the holotype (lv): H 13.0 mm, W 12.5 mm and figured paratype (rv): H 11.6 mm, W 11.8 mm. Distribution: Gulf of Aden. Remarks: The most similar species is Propeamussium siratama (OYAMA in KURODA 1951) recorded from Japan (100–1020 m) (OKUTANI 1966: 8; HIGO & GOTO 1993: 571) and Indonesia (234–467 m) (DIJKSTRA & KASTORO 1997: 253). P. siratama differs from the present species in being smaller (up to c. 12 mm high), in having weaker sculpture on the left valve, in having more internal ribs (usually 8, sometimes with a few rudimentary interstitial riblets), and in colour (left valve opaque or whitish transparent). Also rather similar is Propeamussium malpelonium (DALL 1908), recorded from the tropical eastern Pacific. P. malpelonium differs in having a more prominent sculpture on the entire disc of the left valve and in having 11 internal ribs. This species is recorded only from abyssal depths, 2690–4505 m (GRAU 1959: 14). Propeamussium steindachneri (STURANY 1901) recorded from the Red Sea and Indian Ocean (439–457 m) (OLIVER 1992: 73) differs from P. arabicum in having a more oblique shape, smooth left and right valves, fewer internal ribs (usually 6), smaller auricles, and creamy and white dots on the left valve. Etymology: Arabicus (Lat., adjective) = Arabian.» HENK H. DIJKSTRA & ARIE W. JANSSEN, 2013
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