Parvamussium musorstomi Dijkstra, 2001
DIJKSTRA, H. H. 2001. Bathyal Pectinoidea (Bivalvia: Propeamussiidae,Entoliidae and Pectinidae) from Wallis and Fortuna Islands, Vanuatu Archipelago and New Caledonia.. In P. Bouchet & B. A. Marshall (Eds.), Tropical Deep-Sea Benthos, Volume 22, Mémoires du Muséum National d'Histoire Naturelle 185: 73-95.. [p. 83, figs. 25, 26]
2001 Parvamussium musorstomi Dijkstra, 2001
H. H. Dijkstra, 2001, figures 17-32.
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«TYPE MATERIAL. — Holotype (Iv) MNHN.
TYPE LOCALITY. — Waterwitch Bank (Wallis and Futuna EEZ). 12°31.4' S, 176°39,6' E. 500 m [MUSORSTOM 7, sta. DW5291].
DISTRlBUTlON. — Waterwitch Bank (Wallis and Futuna EEZ). 500 m.
DESCRIPTION. — Shell small (up to ca 8 mm high). fragile. semi-transparent almost orbicular, equilateral, auricles nearly equal in size, umbonal angle about 100°. Transparent. opaque near umbonal area, with scattered white maculations, most frequent near ventral margin.
Prodissoconch ca 210 μm in height. Left valve rather flat, smooth, glossy and very weakly concentrically undulated in early growth stage. Weak commarginal growth lines near ventral margin. Anterior auricle wilh fine, irregularly spaced, commarginal lamellae near anterior margin, near umbonal top smooth; posterior auricle smooth, very weak commarginal lamellae near posterior margin and disk flank. Hinge line straight, rather prominent auricular crura, resilifer triangular and somewhat oblong. Internal lirae 19, plus 3 small rudimentary interstitial riblets. Dimensions of holotype: H 8.3 mm. L 9.0 mm. REMARKS. — The most closely related species is Parvamussium carbaseum Dijkstra, 1991, recorded from the Flores and Banda seas (Indonesia). P. carbaseum has more prominent sculpture on the left valve with radial riblets and closely spaced commarginal lamellae (P. musorstomi is almost smooth), and the anterior auricle has coarse commarginal lamellae (weak and delicate in P. musorstomi). The internal lirae are similar in number, P. musorstomi (19 + 3 rud.) having a few more than P. carbaseum (17 + 3 rud.). Moreover, P. carbaseum is nearly opaque whereas P. musorstomi is translucent.
The Indo-Pacilic Parvamussium scitulum (E. A. Smith. 1885), also recorded from Wallis and Futuna, also has a nearly flat left valve like P. musorstomi, but is more strongly sculptured on the left valve with fine radial striae and more prominent commarginal lamellae on the anterior auricle (DIJKSTRA, 1995: 32). The internal lime are fewer in number (9- 10). P. scitulum is also more opaque and colourful with yellow-brown maculations. Parvamussium pauciliratum (E. A. Smith, 1903), recorded from the Indo-Southwest Pacific, has also a nearly flat left valve and is also smooth like P. musorstomi, but it lacks the internal Iirae (only a few rudimentary are usually present). P. pauciliratum further differs in being also more colourful and mottled than P. musorstomi. ETYMOLOGY. — After "MUSORSTOM", a contraction of Muséum national d'Histoire naturelle and the Institut Français de Recherche Scientique pour Ie Développement en Coopération (now IRD), which organize cruises to explore the bathyal fauna of the Indo-West Pacific.»
HENK H. DIJKSTRA, 2001
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