Aperiploma, Habe, 1952

Carole, Hickman, S. & Ca, 2014, Paleogene marine bivalves of the deep-water Keasey Formation in Oregon, part IV: The anomalodesmatans, PaleoBios 31 (3), pp. 1-21 : 9-10

APERIPLOMA Habe, 1952

Type species — By original designation, Anatina lena Conrad, 1831 . Holocene, western Atlantic .

Nomenclatural confusion regarding the type species of Cochlodesma Couthouy, 1839 resulted in misapplication of this name to the Pacific Coast Cenozoic species. Although the nomenclaturally correct name is now Aperiploma Habe, 1952 , the type species continues to be Anatina lena , a species that has been freed from synonymy with the eastern Atlantic Mya praetenuis Pulteney, 1799 , the type of Cochlodesma . Vokes (1956) traces the history leading to this rectification of nomenclature. Aperiploma continued to be incorrectly synonymized with Cochlodesma by some authors who remained caught in the “taxonomic tangle” (e.g., Bernard 1989) that requires no further discussion here.

Specimens are frequent in occurrence in cool to cold high latitude faunas of the Pacific Coast Cenozoic, but they are never well preserved and never abundant at any one locality. Shells are typically articulated or partially disarticulated, but they are usually crushed and lacking in any of the very thin outer shell layer. However, the interior layers of nacre preserve the undulating concentric sculpture typical of the genus, and the heavily calcified and buttressed opisthodetic spoon-shaped chondrophore is often the most diagnostic feature of a crushed specimen. Individuals are seldom well enough preserved to be separated from the matrix, which may contribute to collection bias in the field. Specimens in matrix may preserve the original outline of individuals from which original shell material has exfoliated.

Marincovich (1983, p.109) states that at least 32 North Pacific Cenozoic species have been described under Periploma . Most of these are from the northwestern Pacific. Assignments to subgenera and species comparisons of the Asiatic Cenozoic taxa will be essential to reconstructing the high-latitude cold-water history of the group.

Stratigraphic range —Eocene to Holocene.