A fossil diatom species, Stephanodiscus akutsui sp. nov., is described from Middle Pleistocene lacustrine sediments of the Miyajima Formation of the Shiobara Group in Tochigi Prefecture, central Japan. Stephanodiscus akutsui is characterized by a valve face with concentric undulation, a shallow mantle, bi- to four-seriate fascicles at the valve margin, zero to two valve face fultoportulae, a single rimoportula, and valves often linked by spines into chains. The combination of morphological characteristics of S. akutsui differs from other related Stephanodiscus species.
2016 The Japanese Society of Diatomology