Paleocene and Miocene Thyasira sensu stricto (Bivalvia: Thyasiridae) from chemosynthetic communities from Japan and New Zealand

A new species of bivalve, Thyasira (Thyasira) beui, is described from lower to middle Miocene hydrocarbon seep deposits from the North Island of New Zealand. T. (T.) nakazawai Matsumoto, 1971 is redescribed from lower Miocene seep deposits in central Honshu of Japan, and T. (T.) sp. from Paleocene wood-fall communities in eastern Hokkaido is described as the first Thyasira sensu stricto in Japan of this age. As the genus Conchocele replaced the niche of Thyasira sensu stricto at seep sites from the Eocene in Japan, the occurrence of T. (T.) nakazawai is an exceptional occurrence of this genus at younger seeps in Japan. In contrast, Conchocele disappeared from New Zealand waters from the end of the Paleocene, leaving Thyasira sensu stricto as the sole thyasirid taxon at New Zealand Cenozoic seep sites.