Cell body flat, large, variable in shape, longer than wide; strong constriction at center;
each semicell with several notches; cell wall with many short spines
(Illustrations of The Japanese Fresh-water Algae, 1977).
Micrasterias thomasiana Archer var. thomasiana,
cell body 223 μm long, 190 μm wide, L/W=1.2, isthmus 28 μm wide,
x 400, x 640, Yacho-no-mori marsh (near road sign No. 4), Sukawa highland, Kurikoma mountain, Higashi-naruse village, Akita Pref., Japan, July 24, 2005 by Y. Tsukii
150 μm; x 400 :
94 μm; x 640