Both Azpeitia endoi and Azpeitia tabularis, which are referred to the Azpeitia tabularis group, are described based on light microscope and SEM observations. Samples came from living material collected on the KH99-3 cruise in the Bering Sea, from fossil Pliocene and Pleistocene material in DSDP Holes 579A and 580 in the northwest Pacific Ocean, and from the Middle Miocene of the Oga Peninsula, northeast Japan. Both these species occurred in the Middle Miocene, and A. endoi has the central depression which is common feature in the genus Azpeitia, while A. tabularis does not. Since A. tabularis does not posses the central depression, A. endoi is considered to represent the ancestral condition for A. tabularis.

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