Parvamussium retiolum 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 : 138

Parvamussium retiolum Dijkstra, 1995

Figs 8C,E,K, 9

Parvamussium retiolum Dijkstra, 1995b: 29 , figs 39–42, 97; Dijkstra, 2001: 85; Dijkstra & Marshall, 2008: 10, figs 8A–G, 9; Dijkstra & Maestrati, 2008: 93; Spencer et al., 2009: 198; Dijkstra & Maestrati, 2013b: 473.

Type data. Holotype (pr) MNHN Moll 21171 . Paratypes (39pr+6v): 35 MNHN Moll 21172, 2 C.201713, 2 ZMA Moll. 395026, 2 NMNZ M.268537, 2 NSMT-Mo70541, 2 USNM890860. Type locality: Coral Sea, Chesterfield Is., 19°47'S 158°44'E, alive, 685–700 m (MUSORSTOM 5 stn CP 363) .

Additional material examined. — AUSTRALIA: QUEENSLAND: SE of Swain Reefs ,22°20'09"– 22°26'16"S 153°17'05"E,dead, 187 m (1 v,C.462543); E of Lady Elliott Island, 24°0' S 153°06'E, dead, 476–531 m (4 v, C.165535). WESTERN AUSTRALIA: SW of Cape Naturaliste, 33°44.5' S 114°26.1'E, dead, 183–238 m (3 v, C.165545); W of Garden Island, 32°15'S 115°03'E, dead, 250–258 m (1 v, C.165550); W of Rottnest Island, 31°0'S 114°51'E, dead (1 v, C.165548); 80 n. ml NNE of Port Hedland, 19°03.6' – 19°04'S 119°03.4' – 119°05'E,dead, 82 m (3 v, C.157711); N of Port Hedland, 18°40'S 117°55'E, dead, 150 m (1 v, C.157679); c. 240 ml NE of Broome, 14°37'S 123°40'E,dead, 80 m (19 v, C.165494 [in part]); c. 140 ml N of Cape Leveque, 14°29'S 123°03'E,dead, 124 m (many v [atypical],C.165493). CORAL SEA:Elizabeth Reef, 29°53.82' S 159°01.65'E, alive, 420 m (1 pr, C.165246). —NEW CALEDONIA: S of Ile des Pins, 22°50'S 167°34' E, dead, 274 m (many v, C.165441; 4 v, C.165439); 4 ml S of Ile des Pins, 22°50'S 167°34'E, dead, 275 m (16 v, C.165443 [in part]; 1 v, C.165442 [in part]; 5 v, C.165444) .

Description. Shell up to c. 16 mm high, fragile, inequivalve, inequilateral, left valve slightly more convex than right, translucent white, auricles unequal, umbonal angle c. 95°. Inner surface with 10 riblets, plus 1 posterior auricular riblet and 4 rudimentery auricular riblets on left valve and 3 on right, ends of riblets somewhat nodose.

Left valve sculptured with delicate commarginal lamellae crossing closely spaced radial riblets, somwhat coarser near umbonal area than elsewhere, more delicate near ventral margin.Auricles with fine radial riblets crossed near margin by fine commarginal lamellae.

Right valve with regular commarginal lirae, closely spaced near umbonal area, more widely spaced near ventral margin. Microscopic interstitial radial scratches near margins. Auricles with commarginal lamellae, more prominent anteriorly. Strongly developed scales on anterodorsal margin. Byssal notch narrow.

Habitat. Living on the continental shelf and in the bathyal zone, free amongst soft sediment.

Distribution. Chesterfield Islands , Coral Sea, 620–700; New Caledonia, 720–800 m (Dijkstra, 1995b, 2001); New Zealand: many lots listed by Dijkstra & Marshall (2008: 10, fig. 9) from the Norfolk Ridge N of Norfolk Island (26°25.2'S 167°11.2'E, 714–756 m, 11 v, NMNZ M.171056) to South Ritchie Trough, off Mahia Peninsula, central E North Island (39°58.59'S 178°14.18'E, alive, 990 m, 2 pr, NIWA V466), in 316–1000 m (Dijkstra & Marshall, 2008: 11, fig. 9); Fiji, 310–699 m; Tonga, 391–510 m (dead) (Dijkstra & Maestrati, 2008). Now also Queensland and Western Australia. Maximum depth range of live-taken specimens is 310–1000 m. Present specimens in 82–531 m, alive in 420 m.

Remarks. Parvamussium retiolum is closely similar to P. maorium , but differs in the sculpture of the left valve ( P. maorium is smooth on the central part of the disc and radially sculptured laterally, P. retiolum commarginally and radially sculptured throughout). Other morphological characters are very similar.

Parvamussium retiolum is a new record for Australia.