Mollusks from late Mesozoic seep deposits, chiefly in California.

Abstract

Twenty-nine mollusk species from Late Jurassic to Eocene hydrocarbon seep deposits from California (USA), Japan, New Zealand, and Barbados are described and illustrated. Twenty species belong to Gastropoda and nine to Bivalvia. Seven new species, three new genera, and one new family are introduced. The gastropod Hikidea gen. nov. includes smooth-shelled Cantrainea-like colloniins from Cretaceous hydrocarbon seeps and plesiosaur falls. Hikidea osoensis sp. nov. is the oldest species of this genus. Chilodonta? reticulata sp. nov. is a distinctive vetigastropod though its supraspecific position is unclear. Phanerolepida onoensis sp. nov. is the first species of this colloniin genus from a seep deposit. We describe two new genera of Hokkaidoconchidae: Abyssomelania gen. nov. and Ascheria gen. nov.; this family includes now four genera (including Hokkaidoconcha and Humptulipsia) and ranges from the Late Jurassic to the Eocene. Abyssomelania is characterized by a large, high-spired shell and unusual widely-spaced prosocline riblets (here called abyssomelaniid riblets). Abyssomelania is represented by two new species: A. cramptoni sp. nov. from the Late Cretaceous of New Zealand and A. campbellae sp. nov. from the Early Cretaceous of California. Ascheria gen. nov. is characterized by a large high-spired cerithiform shell, a subsutural constriction, and mostly reticulate ornament. Two nominate species are included: Ascheria gigantea (Kiel et al., 2008) and A. eucosmeta (Ascher, 1906), both of Early Cretaceous age. Two further species potentially belonging to Ascheria from the Eocene of Barbados are reported in open nomenclature and are re-illustrated and re-described for comparison. Humtulipsia nobuharai sp. nov. is described based on specimens from the Campanian-Maastrichtian Sada Limestone seep deposit in Japan. The new family Paskentanidae fam. nov. is introduced for the genera Paskentana and Atresius. The species of this family are characterized by thin-shelled, broad to high-spired littoriniform adult shells and juvenile teleoconchs with a subsutural ramp. Paskentana hamiltonensis sp. nov. is described from the Early Cretaceous of California. Ataphrus is considered to represent a nomen dubium because its type species is poorly preserved and there are uncertainties regarding its type locality and age. The bivalves reported herein belong to known species, but our new material revealed additional characters, and/or their supraspecific position is revised and new combinations are proposed: Solemya stantoni Vokes, 1955 is transferred to Acharax, Nucula gabbi Stanton, 1895 is transferred to Leionucula, Pecten complexicostata Gabb, 1869 is transferred to Lyriochlamys, Astarte californica Stanton, 1895 is transferred to Neocrassina, Astarte trapezoidalis Stanton, 1895 is transferred to Oxyeurax, and Corbula? persulcata Stanton, 1895 is transferred to Cuspidaria?