Actinocyclus setanensis sp. nov., a new freshwater diatom from the early Miocene sediment in Setana, southwestern Hokkaido, Japan

抄録

Actinocyclus setanensis sp. nov., is described from an early Miocene freshwater sediment of the Futoro Formation located in Setana Town southwestern Hokkaido, Japan. The species has a relatively small round valve face with radial to vague fasciculate areolae rows, pseudonodulus located on valve face/mantle boundary and two to three (rare cases four) stalked rimoportulae, thick and bulged externally with small round openings. Within, we compare the differences between other related Miocene freshwater Actinocyclus taxa and propose it as a new species. The taxon is described with accompanying light and scanning electronic microscope photographs.