Parvamussium lamprelli, Dijkstra & Beu, 2018

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 : 133-135

Parvamussium lamprelli sp. nov.

Figs 5, 7F–J

Holotype (pr) (H 8.9 mm, L 9.4 mm, D 2.3 mm) QM MO.17961: QLD, 18°09'S 148°31'E, alive, 1103–1115 m, epibenthic sled, 08.V.1986 (James Cook University Cidaris I stn 11.3) . Paratypes (pr): seven paratypes from the same locality, 6 QM MO.17734, 1 ZMA Moll. 409001 .

Description. Shell up to c. 9 mm high, fragile, circular, weakly inflated, almost equally convex, inequivalve, equilateral, auricles subequal, umbonal angle about 110°; hyaline, whitish.

Both valves with 12–13 narrow internal riblets, commencing 2 mm below umbo and extending to ventral margin, with narrow marginal apron 1 mm wide; 3–5 rudimentary interstitial riblets near margin, one auricular riblet on each auricle. External sculpture clearly visible from interior.

Left valve smooth, glossy, translucent in early growth stage to c. 4 mm high, later bearing latticed sculpture with numerous, very closely spaced, delicate commarginal and radial lirae extending to ventral margin. Auricles with fine, closely spaced commarginal lamellate riblets and a few very weak radial lirae (2 on anterior auricle and 4–5 on posterior).

Right valve smooth and translucent to c. 2 mm high, later with evenly spaced commarginal lirae, c. 8 per mm in central part of disc. Auricles with commarginal lamellae, more prominent on anterior and more closely spaced on posterior. Dorsal margin straight, with some scales, scales more prominent on anterior auricle. Byssal fasciole small, byssal notch present.

Discussion. Parvamussium lamprelli is morphologically closest to P. multiliratum Dijkstra, 1995 , also recorded here from Queensland and known from the Coral Sea eastwards

Figure 7. A–E, Parvamussium conspectum Dijkstra & Kastoro , separate valves,AM C.462542, E of Swain Reefs, QLD, 22°26'16"S 153°17'05"E, 187 m; lv auricles exterior (A), rv anterior auricle exterior (B), rv exterior (C), lv exterior (D), rv interior (E). F–J, Parvamussium lamprelli sp. nov., 2 paratypes, QM MO17734, JCU Cidaris I stn 11.3, N QLD, 18°09'S 148°31'E, 1103–1115 m; rv anterior auricle exterior (F), rv interior (G), lv anterior auricle exterior (H), rv exterior (I), lv exterior (J). Scale bars represent 0.5 mm (A, B), 2 mm (C–E), 1 mm (F–H), 4 mm (I, J).

to Vanuatu. The two species are very similar in shape, size and internal riblets, and both have a smooth, glossy disc in the early growth stage and are similarly coloured, but differ strongly in sculpture of the left valve. Parvamussium lamprelli has fine latticed sculpture of closely spaced commarginal and radial lirae, whereas P. multiliratum has only widely spaced commarginal lirae. No specimens with intermediate sculpture have been observed.

Another similar-looking species is Parvamussium cassium Dijkstra, 1991 , known from Indonesia. Parvamussium cassium is similar in size and shape, but differs from P. lamprelli in having more widely latticed sculpture on the left valve, a longer anterior auricle on the right valve, and in lacking fully developed internal riblets.

Parvamussium retiaculum Dijkstra, 1995 , known from New Caledonia and Wallis and Futuna, differs from P. lamprelli in having more widely latticed sculpture on the left valve, a more oval shape, a larger anterior auricle, and broader internal riblets.

Parvamussium retiolum Dijkstra, 1995 , known from the Chesterfield Islands , New Caledonia, Wallis and Futuna, and Vanuatu, also has fine latticed sculpture on the left valve, which is coarser than that of P. lamprelli , but these two species otherwise differ strongly in size ( P. retiolum up to 16 mm high, P. lamprelli up to 9 mm), in shape ( P. retiolum oval and oblique, P. lamprelli circular), and in the much larger anterior auricle and broader internal riblets that commence earlier in P. retiolum than in P. lamprelli .

Habitat. Present specimens live-taken from soft sediment in the bathyal zone.

Distribution. So far known only from the type locality.

Etymology. Named after the late Kevin Lamprell, in honour of his work on the Australian Bivalvia.