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Evolution and distribution of the genus Mya, and Tertiary migrations of Mollusca

1965; United States Government Publishing Office; Linguagem: Inglês

10.3133/pp483g

2330-7102

F. Stearns MacNeil,

Marine Biology and Ecology Research

Two genera, Mya, a pelecypod, and Neptunea, a gastropod, were selected as vehicles for a study of late Tertiary to Recent faunal migrations from the Pacific to the Atlantic Ocean by way of the Arctic Ocean because they are mollusks of large size, and because they have unlike larval stages; Mya has small currentborne pelagic larvae, and Neptunea has large bottom-crawling benthonic larvae.This report considers chiefly the genus Mya but also includes a general discussion of Arctic faunal migrations and its bearing on Tertiary paleogeography of the Arctic.Available evidence suggests that during early Tertiary time the Arctic regions either had greatly reduced marine embayments, or they were entirely land.The earliest known marine Tertiary deposits in the high Arctic, found in northern Alaska and Spitzbergen, are of middle or late Miocene age.The first boreal species of Pacific origin to be found in Atlantic Ocean deposits is in the Yorktown Formation of Virginia.The Yorktown Formation is currently assigned to the Pontian (late Miocene) Stage.All known species of the genus Mya are defined and delimited, and an attempt is made to resolve the synonymy of Japanese and American and Pacific and Atlantic species.American, Arctic, and European species are illustrated; Japanese species have been illustrated elsewhere.The geographical distribution of Mya is treated from an evolutionary and migrational standpoint.The genus is restricted to the Northern Hemisphere.Its ancestry is unknown, but it may stem from temperate or subtropical early Eocene forms currently assigned to the genus Sphenia.The earliest known species of Mya occurs in late Eocene or early Oligocene beds of Japan.One indigenous Atlantic species is known.The remaining 16 recognizable taxa are indigenous to the North Pacific.Three, and possibly four, of the Pacific species migrated subsequently by way of the Arctic Ocean to northern Europe and the American Atlantic coast.Nomenclatural and synonymic revisions in this paper include: suppression of the name Mya grewingki nagaoi Oyama and Mizuno as a synonym of M. salmonensis Clark; recognition of M. kusiroensis Nagao and Inoue, M. grewingki Makiyama, and M. cuneiformis (Bohm) in Alaska; acceptance of the name M. japonica Jay in preference to M. oonogai Makiyania for the species occurring in southern Japan; recognition of the name M. elegans (Eichwald) as the valid name for M. crassa Grewingk M. intermedia Dall, and M. profunnior Grant and Gale; recognition of the name M. priapus Tilesius as the valid name for the North Pacific and Bering Sea species identified by most modern Japanese authors as If.japonica Jay; recognition of M. dic-Jcersoni Clark as a close relative of M. elegans; and the recognition of If. pullus Sowerby as a valid species probably most closely related to M. priapus.Two new species are described: Mya fujiei MacNeil, based on M. japonica oonogai