Parvamussium thyrideum (Melvill in Melvill & Standen, 1907)
MELVILL, J. C. & R. STANDEN. 1907. The Mollusca of the Persian gulf, gulf of Oman and Arabian Sea as evidenced mainly through the collections of Mr. F.W. Townsend, 1893 -1906, with descriptions of new species, Part 2. Pelecypoda. Proceedings of the Zoological Society of London, 54: 783-848, pls. 53-56. [p. 809, pl. 55, fig. 10]
1907 Pecten thyrideus Melvill in Melvill & Standen, 1907
J. C. Melvill & R. Standen, 1907,
plate 55. |
«PECTEN THYRIDEUS* Melvill, sp. n. (Plate LV. fig. 10.)
P. testa fere rotunda, delicatissima, alba; valva sinistra paullulum convexa, pulcherrime clathrata, lamellis numerosis concentricis costulisque circa viginti radianiibios, interstitiis quadratis, fenestratis, Iaevibus; auriculis subaequalibus; pagina interna diaphana, laevigata.
Alt. 4, lat. 4, diam. 1-25 mm. (sp. maj.). Hab. Persian Gulf: Gulf of Oman. Lat. 24° 58' N., long. 56° 54' E.; 156 fathoms, shell-sand. A most delicate little Pecten, of which all the specimens we have seen are dissociated valves. It is of the same character and alliance as P. clathratus v. Mart. +, from Christmas Harbour, Kerguelen Island (' Challenger ' Expedition), but the radiating ribs and concentric lamellae aee stronger proportionately. Within, the surface is quite smooth.» * Θνρις ειδος, from the latticed cancellations.
+ Sitzungsb. d. Gesellsch. naturf. Freunde, Berlin, 1881, p. 79. Also vide Rep. 'Challenger' Exp. vol. xiii. p. 305, pl. xxii. figs. 4, 4a. JAMES COSMO MELVILL, 1907
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«Description: Shell small, up to 4.9 mm high, flattened, left valve slightly more convex than right valve, semi-transparent, almost circular, inequivalve, equilateral, auricles unequal, umbonal angle 110°, colour whitish or creamy with white dots. Left valve sculptured with 13–17 prominent, irregularly spaced, antimarginal costae, commencing 1 mm below umbo and extending to ventral margin, and weaker, more regularly and widely spaced commarginal lamellae, with scaly intersections. Secondary interstitial radial riblets developed marginally. Preradial sculpture of delicate, close-set, commarginal lamellae. Auricles with prominent commarginal lamellae and weak antimarginal lirae. Right valve sculptured with very fine, closely spaced, commarginal lirae. Anterior auricle with 5–8 delicate antimarginal lirae, crossed by commarginal lamellae near dorsal margin. Posterior auricle with prominent commarginal lamellae. Byssal notch moderately deep, byssal fasciole small, no ctenolium. Hinge line straight. Resilifer broadly triangular. Variable rudimentary internal radial riblets developed submarginally or even absent.
Distribution: Red Sea, Gulf of Aden, Arabian Sea and Persian Gulf. Sublittoral to bathyal depths. Living on soft sediments (mud, muddy sand or sand with shellgrit). Remarks: The present specimens from the Red Sea and Gulf of Aden are similar to the type material. However, most of the adult specimens have internal rudimentary radial riblets, which are lacking in the type material. These riblets are strongly variable and are absent in juveniles. A somewhat similar species from the Indonesian Archipelago is Cyclopecten cancellus DIJKSTRA1991, which has more reticulate sculpture of prominent antimarginal costae and commarginal lirae on the left valve with fewer intercalated secondary riblets. The internal ribs are absent, but it is possible that in larger specimens (larger than 3.5 mm high) these rudimentary riblets are present as in the present species. Further material is required to be certain that C. cancellus is correctly referred to Cyclopecten.» 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. 196, 197]
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Parvamussium thyrideum (Melvill in Melvill & Standen 1907); H. H. Dijkstra & A. W. Janssen, 2013, Bathyal and abyssal Pectinoidea from the Red Sea and Gulf of Aden, figures 46, 47.
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