Propeamussium de Gregorio, 1884

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 : 121

Propeamussium de Gregorio, 1884

Propeamussium de Gregorio, 1884: 119 (proposed as a subgenus of Pecten ). Type species (by original designation): Pecten (Propeamussium) ceciliae de Gregorio, 1884 ; Miocene, Sicily, Italy.

Paramusium Verrill, 1897: 72 . Type species (by original designation): Amussium dalli E. A. Smith (1885: 308); Recent, off Bermuda, W Atlantic, 796 m.

Occultamussium Korobkov, 1937: 56 (proposed as a subgenus of Amusium ). Type species (by original designation): Pecten semiradiatus Mayer, 1861 ; upper Eocene, Tyrol, Austria.

Pseudopalliorum Oyama, 1944: 244 (proposed as a subgenus of Propeamussium ). Type species (by original designation): Pecten interradiatus Gabb (1869: 199, 251); Eocene, E of New Idria, San Bernardino County, California, U.S.A.

Bathyamussium Oyama, 1951: 79 (proposed as a subgenus of Ctenamusium ). Type species (by original designation): Amussium jeffreysii E. A. Smith (1885: 310); Recent, N Sulu Sea, Philippine Islands , 686 m.

Micramussium Oyama, 1951: 80 (proposed as a subgenus of Ctenamusium ). Type species (by original designation): Ctenamusium (Micramussium) siratama Oyama (1951: 80) ; Recent, Sagami Bay, Japan, 234– 291 m.

Flavamussium Oyama, 1951: 81 (proposed as a subgenus of Parvamussium ). Type species (by original designation): Amussium caducum E. A. Smith (1885: 309); Recent, W of Luzon, Philippine Islands , 1280 m.

Luteamussium Oyama, 1951: 82 . Type species (by original designation): Amussium sibogai Dautzenberg & Bavay (1904: 207) ; Recent , Bali Sea, Indonesia, 289 m.

Diagnosis. Shell almost equivalve, fragile, rather small in most species, translucent in most species, laterally compressed, gaping along lateral margins; left valve smooth or sculptured with fine radial and/or commarginal riblets or striae, right valve with commarginal lines or lirae; auricles almost equal to equal; byssal notch moderately slight; ctenolium lacking; internal riblets commence in early ontogeny and extend to near the central region or to the pallial line.

Distribution. Eocene?–Recent. Cosmopolitan, 275–2740 m ( Waller, 1971). Waller (2006a) thought that Jurassic species previously included in Propeamussium would be better assigned to Parvamussium . Schneider et al. (2013: 221) also stated that “All Jurassic to Oligocene propeamussiids that have been studied thoroughly to date belong to Parvamussium … Propeamussium did not evolve earlier than the Miocene.” D. Jablonski (pers. comm. 27 Jun 2017) pointed out that P. interradiatium (Gabb 1869) , occurring in the Lutetian– Bartonian (Eocene) Tejon Formation, California, USA ( Stewart, 1930: 123; Addicott, 1971; Moore, 1984: 7) “seems a potential species of Propeamussium given the equal auricles and nature of the internal ribs”. Further study is required of pre-Miocene records of these subtly distinct genera before the range of Propeamussium is certain, but a range from at least Eocene onwards seems likely.

Discussion. Grau (1959) restated the original diagnosis of Propeamussium de Gregorio, 1884 , and of the type species P. ceciliae , with a translation into English. The type specimen subsequently was figured by de Gregorio (1898: pl. 4, figs 10–12). Gregorio’s figures 13 and 14, also mentioned by Grau (1959: 9), do not show the type species. Hertlein (1969: N350) supposedly refigured the right [sic] valve of the holotype, although North (1951b: 123) reported that he could not trace the holotype.

Grau (1959: 9) placed Paramussium, Pseudopalliorum , Flavamussium and Luteamussium in the synonymy of Propeamussium , and Hertlein (1969: N350) subsequently added also Occultamussium and Actinopecten Bonarelli, 1951 with a question mark. Hayami (1988a) enumerated also Parvamussium Sacco, 1897a (type species: Pecten duodecimlamellatus Bronn, 1832: 624 ), Ctenamussium [sic] Iredale, 1929 (type species: Amusium thetidis Hedley, 1902: 304 ), Glyptamusium Oyama, 1944 [sic] (= Glyptamusium Iredale, 1939 ) (type species: Amussium torresi E. A. Smith, 1885: 311 ), Bathyamussium Oyama, 1951 (type species: Amussium jeffreysii E. A. Smith, 1885: 310 ) and Micramussium Oyama, 1951 (type species: Ctenamusium (Micramussium) siratama Oyama, 1951: 80 ) as synonyms of Propeamussium . The type species of Ctenamusium and Glyptamusium are morphologically inseparable from Parvamussium , whereas the type species of Bathyamussium and Micramussium are more nearly similar to the morphological characters of Propeamussium .

For the distinctive shell microstructure of Propeamussiidae see Waller (1972b) and Schein (1989).