Actinocyclus hiramakiensis, a new freshwater diatom from Early Miocene sediment, Gifu Prefecture, Japan

Abstract

Actinocyclus hiramakiensis sp. nov. is described from Early Miocene freshwater sediment of the Hiramaki Formation located in southern Gifu Prefecture, Japan. The species has a round valve face with concentric undulation, radial areola rows usually irregular or loosely packed with areolae in valve center, areolae with external and internal vela, a pseudonodulus located on the valve face/mantle boundary as well as some stalked rimoportulae with long tubes and labia running parallel to the tube axes. The new species has characteristics similar to those of the genus Actinocyclus, but in other ways it differs from existing Actinocyclus species. Light and scanning electronic microscope photographs are provided along with the description.