Genus: Ovoid, firm; dorsal side convex, ventral side flattened; dorsal surface ridged; adoral zone reduced or rudimentary; macronucleus U-shaped or in two rounded parts (Kudo, 1966). No mariginal or caudal cirri; common genus (Carey, 1992). Species: Ovoid, small and convex on the right; up to 45 μm long, body outline smooth; peristome at posterior expanded to form a swelling; dorsal ridges vary in shape and number; 7 ventral, 5 transverse cirri; macronucleus C-shaped (Carey, 1992).

50 μm 100 μm 150 μm; x 400

31 μm 63 μm 94 μm; x 640

Aspidisca cicada (formerly A. costata),a dividing cell, x 640, Japan 1998 by Y. Tsukii
31 μm 63 μm 94 μm; x 640

Aspidisca cicada, x 400, x 640, Japan November 1998, by Y. Tsukii
50 μm 100 μm 150 μm; x 400 : 31 μm 63 μm 94 μm; x 640

A. costata (Dujardin, 1842 ?) Kahl, 1932 (synonym: A. cicada ?): Ovoid; 25-40 μm long, 17-28 μm wide; outline smooth but posterior swell; 6 longitudinal dorsal ridges; 7 frontoventral, 5 transverse cirri; macronucleus horseshoe-shaped; fresh water (Gensei-dobutu-zukan, 1981).

A. cicada (Müller, 1786) Claparède and Lachmann, 1858 (Syn. Aspidisca costata (Dujardin, 1841 ?) Stein, 1859; Aspidisca sulcata Kahl, 1930-5): Ovoid; 45 μm long; outline smooth but posterior swell; longitudinal dorsal ridges vary in shape and number; 7 frontoventral, 5 transverse cirri; macronucleus C-shaped (Carey, 1992).

A. polypoda (Dujardin, 1841) Kahl, 1930-5: Ovoid; 55 μm long; outline smooth but 7-8 dorsal ribs; 7 frontoventral, 6 transverse cirri; macronucleus horseshoe-shaped (Carey, 1992).