Parvamussium squalidulum Dijkstra, 1995

Dijkstra, Henk H. & Beu, Alan G., 2018, Living Scallops of Australia and Adjacent Waters (Mollusca: Bivalvia: Pectinoidea: Propeamussiidae, Cyclochlamydidae and Pectinidae), Records of the Australian Museum (Rec. Aust. Mus.) 70 (2), pp. 113-330 : 141

Parvamussium squalidulum Dijkstra, 1995

Figs 10E,J–M, 11

Parvamussium squalidulum Dijkstra, 1995b: 32 , figs 47–50; Dijkstra & Kastoro, 1997: 262, figs 79–82; Dijkstra & Marshall, 1997: 81, pl. 4, figs 5–10; Dijkstra & Marshall, 2008: 12, figs 10A–E, 11; Dijkstra & Maestrati, 2008: 94; Xu & Zhang, 2008: 78, fig. 216; Spencer et al., 2009: 198; Dijkstra & Maestrati, 2010: 339; Dijkstra, 2011: 42, pl. 1016, figs 1a–b; Dijkstra & Maestrati, 2013b: 474.

Type data. Holotype (pr) MNHN Moll 21169 . Paratypes (3 pr + 10 v): 2 AM C.201714, 3 ZMA Moll.395027, 6 MNHN Moll 21170, 2 USNM 886342. Type locality: Lord Howe Rise, Kelso Bank , 24°11'S 159°35'E, alive, 270 m (MUSORSTOM 5 stn DW 277) .

Additional material examined. — AUSTRALIA: QUEENSLAND: E of GBR, 17°22'S 146°48'E, alive, 296–303 m (9 pr [smooth var.], QM MO.17747; 7 pr [smooth var.], QM MO.17943) . WESTERN AUSTRALIA: S of Rowley Shoals , approx. 17°35'S 118°56' E, dead, 260 m (1 v, WAM418.91 ) .— NEW CALEDONIA:4 ml S of Ile des Pins , 22°50'S 167°34'E,dead, 275 m (2 v, C.165443 [in part]) . TASMAN SEA: Lord Howe Shelf , 31°36'S 159°09'E, dead, 35 m (15 v, C.461383 [in part]) ; Lord Howe Shelf , 31°43' S 159°04'E, dead, 98 m (3 v,C.463023) ; Lord Howe Shelf , 31°44'S 159°04'E, alive, 117.5 m (1pr, 13 v, C.463024) ; Lord Howe Island, Balls Pyramid , 31°46'S 159°09'E, dead, 157.5 m (12 v, C.463025).

Description. Shell up to c. 11 mm high, fragile, semitranslucent, almost circular, inequivalve, inequilateral, left valve slightly more convex than right, auricles unequal in size, umbonal angle c. 125°. Inner surface of both valves with 10 radial riblets, with a few interstitial rudimentary riblets in some specimens. One auricular riblet on posterior auricle, absent on anterior. Left valve cream, with white and orange-brown maculations, right valve semi-translucent white, glossy.

Left valve sculptured with numerous unevenly spaced scaly radial riblets, increasing in number towards ventral margin, with delicate intercostal commarginal lamellae, more closely spaced near ventral margin than elsewhere. Both auricles with commarginal lamellae, anterior auricle with 3 very weak radial riblets, absent from posterior. Dorsal margin straight.

Right valve with minute commarginal lirae near lateral margins, absent from central part of disc. Delicate, closely spaced commarginal lamellae near ventral margin. Anterior auricle with 5 radial riblets crossed by commarginal lamellae, posterior auricle with delicate lamellae near disc flank. Byssal notch narrow.

Habitat. Living on the outer continental shelf and in the bathyal zone, free on soft sediment (sand and mud).

Distribution. Eastern Indonesia, 124–850 m (dead) (Dijkstra & Kastoro, 1997);

Chesterfield Islands , Coral Sea, 270 m; Loyalty Islands , 380 m (dead); Vanuatu, 325–400 m ; Wallis and Futuna Islands , 210–330 m (dead) ( Dijkstra , 1995b, 2001) ; Kermadec Islands , 302 m (Dijkstra & Marshall, 1997; Dijkstra & Marshall, 2008: 12, fig. 11); Fiji, 280–296 m ; Tonga, 523–806 m (Dijkstra & Maestrati, 2008) ; Austral Islands , 112–121 m (Dijkstra & Maestrati, 2010). Maximum depth range of live-taken specimens is 112– 806 m. Present specimen from Queensland (296–303 m, alive), New South Wales (117.5 m, alive), and Western Australia (dead in 260 m) .

Remarks. The present specimens from Western Australia are identical to the type specimens.

Parvamussium squalidulum is a new record for Australia.