Parvamussium Sacco, 1897

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 : 128-129

Parvamussium Sacco, 1897

Parvamussium Sacco, 1897a: 102 . [Proposed as a subgenus of Amussium Herrmannsen, 1846 (invalid emendation of Amusium Röding, 1798 )]; no diagnosis provided, but type species designated. Parvamussium Sacco, 1897b: 48 (diagnosis). Type species (by original designation): Pecten (Pleuronectes) duodecimlamellatus Bronn (1832: 624) ; upper Miocene, Tabbiano, northern Italy.

Variamussium Sacco, 1897a: 102 . [Proposed as a subgenus of Amussium Herrmannsen, 1846 ]; no diagnosis given, but type species designated. Variamussium Sacco, 1897b: 49 (diagnosis). Type species (by original designation): Amussium cancellatum E. A. Smith (1885: 315); Recent, off Bermuda, W Atlantic, 796 m.

Ctenamusium Iredale, 1929: 164 . Type species (by original designation): Amusium thetidis Hedley (1902: 304) ; Recent , off Port Kembla, New South Wales, Australia, 115–137 m.

Glyptamusium Iredale, 1939: 370 . Type species (by original designation): Amussium torresi Smith (1885: 311); Recent, E of Cape York, QLD, Australia, 283 m.

Squamamussium Oyama, 1944: 245 . [Proposed as a subgenus of Propeamussium ]. Type species (by original designation): Amussium squamigerum Smith (1885: 312); Recent, off E Puerto Rico, West Indies, 713 m.

Polynemamussium Habe, 1951: 72 . [Proposed as a subgenus of Parvamussium ]. Type species (by original designation): Pecten intuscostatus Yokoyama (1920: 156) ; Pleistocene, Kami-Miyata, Miura City, Kanagawa Prefecture, Japan.

Diagnosis. Shell inequivalve, circular to oblique, most species small, to c. 20 mm high, laterally compressed, with no lateral gape; left valve of most species strongly sculptured with radial and/or commarginal riblets or striae, right valve with commarginal lamellae; auricles unequal; byssal notch well-developed; no ctenolium; internal riblets commence in late ontogeny and extend to submarginal or marginal region.

Distribution. Triassic or Jurassic–Recent ( Waller, 2006b, 2011; Schneider et al., 2013; Ros-Franch et al., 2014). Waller (2006b) considered that all Jurassic records of Propeamussium refer to Parvamussium species. He also thought that Triassic records of Parvamussium are too poorly preserved for certain generic assignment, and might

Figure 4. A–C, F, Propeamussium watsoni (Smith) , pair, AM C.165216, ENE of Cape York Peninsula, QLD, 815–825 m; lv exterior (A) and interior (B), rv interior (C) and exterior (F). D, E, G, H, Propeamussium meridionale (Smith) , separate valves, AM C.165413, ORV Franklin stn 89-33, Lord Howe Rise, Tasman Sea, 27°13.34'S 160°43.41'E, 1989 m; rv exterior (D), lv exterior (E), rv anterior auricle exterior (G), lv anterior auricle exterior (H). Scale bars represent 10 mm (A–C, F), 5 mm (D, E), 0.5 mm (G, H).

belong to Filamussium Waller, 2006b . However, Ros-Franch et al. (2014) considered Filamussium to be a synonym of Parvamussium . Further research clearly is required on the time range of Parvamussium . Cosmopolitan, 18–2120 m.

Discussion. Parvamussium differs from Propeamussium mainly in the presence of a byssal notch (no byssus is observed in Propeamussium ), the inequality of the auricles (equal in Propeamussium ), more prominent sculpture (absent or very weak in Propeamussium ), the position and number of internal radial riblets (commencing in early ontogeny and extending to central part in Propeamussium ), and the absence of lateral gapes (present in Propeamussium ).

Grau (1959: 15) and Hertlein (1969: N350) treated Parvamussium as a subgenus of Propeamussium and listed Variamussium , Ctenamusium , Glyptamusium , Xenamussium , Squamamussium , Polynemamussium , Bathyamussium , Micramussium as synonyms of Parvamussium . Hertlein (1969: N350) also mentioned in the synonymy Graptamussium Oyama, 1944, which is an error for Glyptamusium . The morphological characters of Bathyamussium and Micramussium are identical to those of Propeamussium (see remarks under Propeamussium ), and characters of Xenamussium Oyama, 1951 are identical to those of Cyclopecten Verrill, 1897 (see remarks under Cyclopecten ).