Cap-shaped gastropods from Upper Jurassic and Lower Cretaceous deposits of northern East Siberia

Cap-shaped gastropods are first identified in Upper Jurassic and Lower Cretaceous sections of northern East Siberia. They belong to three new genera of the subclass Pectinibranchia ( Boreioconus gen. nov., Nixepileolus gen. nov., and Taimyroconus gen. nov.), which are identified at the species level ( B. bojarkensis sp. nov., N. depressus sp. nov., T. zakharovi sp. nov.), and several species with the open nomenclature. The genus Taimyroconus attributed to the family Calyptraeidae is considered as an ancestral form of the genus Crepidula . The stratigraphic position of each taxon is determined for several sections. The facies confinement, habitat conditions, and ethology of defined genera are considered with the analysis of their geographic distribution.