Pseudamussium challengeri (E. A. Smith, 1891 )

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 : 172

Pseudamussium challengeri (E. A. Smith, 1891)

Figs 26, 29A–B, 31A–B

Pecten challengeri Smith, 1891: 443 , pl. 35, fig. 25.

Chlamys (Veprichlamys) challengeri (Smith) .– Iredale, 1929: 164; Rombouts, 1991: 34.

Chlamys (Chlamys) challengeri (Smith) .–Lamprell & Whitehead, 1992: [20], pl. 8, fig. 46.

Veprichlamys challengeri (Smith) .–Raines & Poppe, 2006: 248, 249, upper figs; pl. 197, fig. 4.

Pseudamussium challengeri (Smith) .–Dijkstra & Marshall, 2008: 70, figs 59A–F, 60; Spencer et al., 2009: 198.

Type data. Lectotype (pr: H 19.0 mm, W 18.4 mm, D 4.6 mm) NHMUK 1889.2.13.1, herein designated; paralectotype (rv) NHMUK 1889.2.13.2. Type locality: off Sydney, 34°13'S 151°38'E, alive, 410 fathoms [750 m] (Challenger stn 164b).

Additional material examined. — AUSTRALIA: NEW SOUTH WALES: E of Cape Three Points , 33°28'– 33°29'S 152°04'– 152°03'E, dead, 457–476 m (1 v, C.155816) ; off Broken Bay , 33°32'– 33°34' S 152°06'– 152°05' E, dead, 823 m (1 v, C.123385) ; E of Broken Bay , 33°32'– 33°38' S 152°0'– 152°04'E, dead, 823 m (1 v, C.310689) ; off Broken Bay , 33°35'– 33°33'S 152°0'– 152°02'E, alive, 823 m (1 pr, C.343929) ; off Sydney , 33°42' – 33°39'S 151°52'– 151°54'E, dead, 457 m (2 v, C.155830) ; off Sydney , 34°05'S 151°43'E, dead, 750 m (1 v, C.339158) ; SE of Botany Bay , 34°21'– 34°16'S 151°24'– 151°28'E,dead, 421 m (2 v,C.102825) ; off Port Kembla , 34°39'– 34°35'S 151°15'– 151°17'E, dead, 466 m (1 v, C.140411; 1 v, C.140414) ; off Port Kembla , 34°42'– 34°38'S 151°14'– 151°18'E, alive, 498–521 m (1 pr, C.135831) ; off Nowra , 34°50'S 151°13'E, dead, 550 m (1 v, C.155801) ; off Shoalhaven Bight , 34°54'– 34°50'S 151°14'– 151°15'E, alive, 988–1006 m (1 pr, C.155803) ; E of Brush Island ,35°28'– 35°33'S 150°50'– 150°47'E,alive, 604 m (1 pr,C.155798) ; E of Ulladulla , 35°31'– 35°36'S 150°47'– 150°44'E, dead, 549 m (1 v, C.310687) ; off Brush Island, Batemans Bay , 35°36'– 35°44'S 150°44' – 150°38'E, dead, 549–586 m (1 v, C.310688) ; E of Brush Island , 35°44'– 35°40'S 150°38'– 150°41'E, dead, 549 m (1 pr, C.105420) ; E of Eden , 36°56'– 36°58' S 150°20'E, dead, 274 m (2 v, C.155797) ; E of Eden , 36°59'– 36°58'S 150°21' – 150°22.7'E, dead, 716–900 m (1 v, C.310686) . VICTORIA: SE of Gabo Island , 37°48'– 37°37'S 150°13' – 150°16'E, dead, 494 m (1 pr, C.134357) . SOUTHAUSTRALIA: off Cape Martin , 38°07'S 140°0'E,dead, 667 m (1 v,C.339157) . WESTERN AUSTRALIA: Albany,off Bald Island , 400–420 m , dead,trawled on sand and mud (2 v, HM);off Albany ,35°23'33"– 35°24' 04"S 118°18'32"– 118°18'22"E,dead, 748–776 m (1 v, WAM S77661 ) .

Description. Shell up to c. 25 mm high, thin, weakly inflated, somewhat prosocline, higher than wide, inequivalve, inequilateral, anterior auricles larger and longer than posterior, umbonal angle c. 100–105°; cream-brown, interior slightly darker, glossy.

Both valves sculptured with about 10 unevenly spaced, rounded, scaly, primary radial costae, commencing c. 2 mm below umbo, increasing by division into c. 20 (left valve) or 30 (right valve) scaly riblets near ventral margin; furrowing interior surface weakly, apart from short, prominent furrows around ventral margin; weak, irregular, commarginal growth costae and plicae also present. Pre-radial stage almost smooth; later with intercostal antimarginal microsculpture. Auricles with 4–6 scaly riblets, weak on posterior auricles, more prominent on anterior ones. Byssal notch rather deep, byssal fasiole broad. Functional ctenolium well-developed, with 5–6 teeth. Hinge teeth weak.

Dimensions. Illustrated specimen: NSW, E of Brush Island, 604 m (AM C.155798): rv: H 18.4, L 17.5 mm; lv: H 18.1, L 17.0 mm; D 4.8 mm.

Habitat. Living in the bathyal zone on soft sediment, probably byssally attached to hard objects, as shown by its well-developed functional ctenolium. Present specimens alive at 498–1006 m.

Distribution. Australian temperate waters, from New South Wales (c. 33°S) to South Australia (c. 38°S); Tasman Sea and New Zealand (Dijkstra & Marshall, 2008: 71–72, fig. 60), as far south as SW of Cape Foulwind, NW South Island (42°10.0'S 170°10.0'E, 610 m, 2 v, NMNZ M.05697).

Remarks. The South African species Pseudamussium gilchristi (G. B. Sowerby III, 1904) resembles P. challengeri in shape and colour, but lacks the intercostal antimarginal microsculpture, which is dominant in P. challengeri . The macrosculpture of both Pseudamussium challengeri and P. gilchristi is extremely variable, ranging from the smooth undulated radial riblets characteristic of the New Zealand morph of P. challengeri to a more complicated sculpture of primary radial costae and secondary riblets, which are covered with spoon-shaped lamellae (Dijkstra & Marshall, 2008: 72).

Iredale (1929) and Rombouts (1991) referred Pseudamussium challengeri to Veprichlamys Iredale, 1929 , presumably because the radial microsculpture is similar to that in Veprichlamys . However, the radial macrosculpture is much more variable than in Veprichlamys , without the regular, even, narrow, widely spaced radial costae characteristic of Veprichlamys . This species more nearly resembles the type species of Pseudamussium , P. peslutrae ( Linnaeus, 1771) , in shape and convexity, in having weak radial sculpture, and in lacking commarginal microsculpture, at least in maturity (Dijkstra & Marshall, 2008: 72).