Parvamussium maorium Dell, 1956

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 : 135

Parvamussium maorium Dell, 1956

Figs 5, 8A–B,H–I,L

Parvamussium maorium Dell, 1956: 20 , figs 30–31 (as Parvamussium maoria [sic]); Powell, 1979: 381, figs 93.1–2; Dijkstra & Marshall, 2008: 9, figs 6E–I, 7; Spencer et al., 2009: 198; Huber, 2010: 224.

Parvamussium maorum [sic] Dell.–Dell, 1962: 75; Dell, 1963: 206.

Type data. Holotype (rv) NMNZ M.09171, 8 paratypes: 4 v NMNZ M.09169, 2 v NMNZ M.010737 and 2 v CMC AQ 169. Type locality: New Zealand, off Otago Peninsula , ENE of Taiaroa Head, Karitane Canyon , 45°37.5'S 171°06.0'E, 476–640 m (Alert stn 54-17).

Additional material examined. — AUSTRALIA: NEW SOUTH WALES: off Newcastle , 32°59' S 152°33.5'E, dead, 381–444 m (1 v, C.165531) ; 28 km E of Little Bay , 33°58.54'S 151°33.38'E, dead, 183–192 m (3 v,C.165526) ; 27.5 ml off Sydney , 33°83.3' S 151°81.7'E, dead, 549 m (7 v + 3 fragm., C.024344) ; off Sydney , 34°04.2'S 151°37.2'E,dead, 384 m (2 v,C.165527) ; off Kiama ,34°38'– 34°33'S 151°16' – 151°17'E,alive, 450–500 m (1 pr,C.165525) ; 44 km E of Nowra , 34°55.79'– 34°56.06'S 151°08.06'– 151°07.86'E, alive, 429–466 m (1 pr, VM F60167 ) ; off Jervis Bay , canyon, 35°08.3'S 151°10'E,dead, 400–1000 m (1 v,C.165532) . VICTORIA: 30 ml S of Cape Everard , 38°18'S 149°17'E,dead, 366 m (11 v,C.165530) ; S of Point Hicks , 38°17.70' S 149°11.30' E, alive, 400 m (3 pr, VM F60150 ; 5 pr, VM F.60153; 2 pr, VM F60161 ) . TASMANIA: Bass Strait,between Cape Everard & Flinders Island , 38°59' S 148°34.1' E, dead, 426 m (4 v, C.165553) ; off Cape Naturaliste , 40°50.6' S 148°46.5'E, dead, 399 m (20 v, C.165528; 5 v, C.165529) ; off Freycinet Peninsula , 41°57.50' S 148°37.90'E, alive, 400 m (7 pr, VM F60152 ) ; off Freycinet Peninsula , 42°0.20' S 148°37.70'E, alive, 720 m (12 pr, VM F60151 ) ; 9.5 ml NE Tasman Island , 43°12.30' S 148°13.45'E, dead, 570.5 m (11 v,C.165534) . TASMAN SEA: Lord Howe Rise , 29°42.06'S 159°48.31'E, alive, 2450 m (1 pr, C.165408).

Description. Shell up to c. 14 mm high, fragile, translucent to almost opaque, inequivalve, equilateral (juvenile), inequilateral (adult), higher than wide, left valve slightly more convex than right valve, auricles unequal in size, umbonal angle c. 90°. Whitish with fine dull white maculations on left valve.

Left valve acline to weakly posteriorly elongate (prosocline), weakly sculptured laterally with unevenly and closely spaced radial riblets, more prominent posteriorly. Central part of disc smooth. Antero-ventrally also with delicate, closely spaced commarginal lamellae. Anterior auricle with commarginal lamellae near disc flank and more dorsally with a few delicate antimarginal riblets, posterior auricle with a few weak antimarginal riblets. Dorsal margin straight.

Right valve sculptured with evenly spaced commarginal lamellae.Auricles somewhat raised dorsally, due to commarginal sculpture. Anterior auricle weakly commarginally sculptured, dorsally more prominent, with one antimarginal riblet near pseudo-fasciole, posterior auricle almost smooth. Byssal notch relatively deep.

Interior of both valves with 10–11 radial riblets, most specimens with 10 riblets, somewhat curved in posterior direction; with a small auricular riblet laterally.

Habitat. Living in the bathyal and abyssal zones, free on soft sediment (muddy sand or mud).

Distribution. New Zealand and Chatham Islands : many lots from throughout the New Zealand EEZ, from Three Kings Rise (31°30.7'S 172°49.8'E, 1216–1385 m; 1 v, NIWA U602) to off Campbell Island (53°29'S 169°48'E, 589–594 m; 1 v NMNZ M.39553), as shallow as 168 m in the Southland fiords, but in 349–1208 m elsewhere (Dijkstra & Marshall, 2008: 9, fig. 7). Now also Tasman Sea and southeastern Australia (New South Wales, Victoria and Tasmania). The live-taken specimen from the Tasman Sea is the only record from an abyssal depth (2450 m). Present specimens from Australia dead at 183–1000 m, alive at 400– 720 m.

Remarks. The present specimens from south-eastern Australia are morphologically identical to the type specimens from New Zealand.

Parvamussium maorium is a new record for Australia.