Abstract
In Japan, two species Arachnoidiscus ornatus and A. ehrenbergii have been reported as the recent species in this genus. They are well known as the epiphyte, and often cover the whole surfaces of seaweeds. Materials collected from 10 localities in Japanese coast show no difference except for the diameter of valve. It is concluded that the Japanese recent entity of Arachnoidiscus can be named under A. ornatus with a synonym of A. ehrenbergii.
