Parvamussium lamellatum Dijkstra & Maestrati, 2013
DIJKSTRA, H. H. & P. MAESTRATI. 2013. Pectinoidea (Bivalvia: Propeamussiidae, Entoliidae and Pectinidae) from the Tarava Seamounts, Society Islands and the Tuamotu Archipelago (French Polynesia). Zoosystema, 35 (3): 361-375, figs. 1-4. [p. 364, fig. 1]
2013 Parvamussium lamellatum Dijkstra & Maestrati, 2013
H. H. Dijkstra & P. Maestrati, 2013, figure 1.
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«TYPE MATERIAL. — Society Islands. Tarasoc, stn DW 3463, 17˚34’S, 149˚54’W, 460-505 m, alive, paratypes 4 spms, 1 lv (MNHN 25697); stn CP 3464, 17˚34’S, 149˚54’W, 460 m, alive, holotype spm (MNHN 25695), paratypes 3 spms, 1 lv (MNHN 25696); stn DW 3476, 17˚29’S, 149˚45’W, 435-490 m, alive, paratypes 3 spms (two MNHN 25698, one ZMA Moll. 398322).
TYPE LOCALITY. — Society Islands, Moorea, 17˚34’S, 149˚54’W, 460-505 m (Tarasoc, stn DW 3463).
ETYMOLOGY. — Left valve covered with lamellae (latin: lamellatus, adjective meaning thinly layered).
OTHER MATERIAL EXAMINED. — Society Islands. Tarasoc, stn DW 3406, 16˚31’S, 152˚32’W, 504-763 m, 1 lv; stn DW 3408, 16˚25’S, 152˚17’W, 437-536 m, 34 lv, 91 rv; stn DW 3415, 16˚34’S, 151˚47’W, 614-730 m, 1 lv; stn DW 3455, 16˚52’S, 151˚20’W, 430-527 m, alive, 1 spm, 3 lv, 3 rv; stn DW 3482, 17˚29’S, 149˚45’W, 440 m, 2 lv; stn unknown, 300-900 m, 1 lv, 1 rv.
Tuamotu Archipelago. Tarasoc, stn DW 3378, 15˚38’S, 146˚51’W, 887-890 m, 1 lv. DISTRIBUTION. — Society Islands and Tuamotu Archipelago, alive at 460 m depth.
DESCRIPTION
Shell up to c. 10 mm in height, fragile, opaque whitish or pigmented with white and creamy dots and streaks, almost circular, inequivalve, nearly equilateral, weakly inflated, left valve slightly more convex than right valve, auricles unequal in shape and size (anterior larger than posterior). Prodissoconch 230 μm long. Left valve sculptured with strongly developed, closely spaced, commarginal lamellae and closely arranged radial rows of imbricated vesicles (damaged on many specimens), which are part of the commarginal lamellate sculpture, commencing at 1.5 mm from dorsal margin (radial rows of vesicles c. 12-15 mm), with increasing intercalated radial row of vesicles to ventral margin (c. 30 mm). Anterior auricle sculptured with prominent, closely spaced, commarginal lamellae and one or two hollow bands, posterior auricle almost identically sculptured with slightly more closely spaced and less prominent commarginal lamellae. Right valve with closely spaced, regularly arranged, weak commarginal lirae, lamellate near ventral margin. Marginal apron (c. 1.5 mm) pressed against left valve, broken off many specimens. Anterior auricle with coarse, closely spaced commarginal lamellae, posterior more delicate. Hinge line straight. Byssal notch shallow, byssal fasciole narrow, ctenolium lacking. Internal riblets (ten and one weak auricular on each side, plus one or two rudimentary in some specimens) commence in early growth stage and extend to ventral submarginal area. Dimensions of the holotype: H 9.5 mm, W 9.7 mm, D 2.2 mm. REMARKS
The present species is morphologically close to Parvamussium australanum, known from the Austral Islands, but differs somewhat in size (Parvamussium lamellatum n. sp. up to 10 mm high, P. australanum up to 12 mm), in having radial rows and intercalated secondary radial rows of vesicles on the left valve, which are lacking in P. australanum (Dijkstra & Maestrati 2010: fig. 2A), in having closely spaced, prominent commarginal lamellae (P. australanum with widely spaced commarginal sculpture), in lacking intercalated radial microsculpture on the left valve (present in P. australanum), in having more prominently developed internal ribs (10 ribs) commencing early ingrowth (P. australanum 12 ribs, commencing later on the central part of the inner surface). Parvamussium undosum Dijkstra, 1991, known from the southwestern Pacific, is similar in shape, size and internal ribs, but differs from P. lamellatum n. sp. by having more delicate and more closely spaced lamellae on the left valve and auricles and by lacking the radial rows of vesicles. Moreover, P. undosum has small solid radial lirae on the left valve that are lacking on P. lamellatum n. sp.» HENK H. DIJKSTRA & PHILIPPE MAESTRATI, 2013
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