Suborder: Ventral cirri not as distinct files, except Gastrostyla.
Family: Frontoventral cirri scattered on forward, mid- and rear areas of ventrum.
Genus: Marginal cirri not confluent at rear; oral cavity wide, expansive; caudal cirri (usually 3) prominent (Illustrated Guide, 1985). Cell body ovoid to elongate, inflexible; large AZM supported anteriorly by a collar; two rows of marginal cirri not confluent posteriorly; strongly-developed frontoventral & transverse cirri present; three long, stiff caudal cilia; dorsal surface ornamented by short rows of cirri; two macronuclei; cyst stage recorded in some species (Carey, 1992).
8 (3 + 2 + 3) frontal, 5 ventral, 5 transverse, 3 caudal cirri.
Species: 100-300 μm long (Kudo, 1966). Elongate, anterior wider than posterior; up to 300 μm long; AZM 1/3 to 1/2 body length; distinctive 3 frontal and 3 long caudal cirri; two ovoid macronuclei (Carey, 1992).
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S. mytilus
225 μm
posterior rounded
Saitama, 1999
S. mytilus
175-200 x 88 μm
posterior truncated
Japan, 1998
S. mytilus
163 μm
posterior truncated
Saitama, 1999
S. mytilus
μm
posterior truncated
Ta river
Ishibashi
Tochigi, 2004
S. mytilus
160 x 65 μm
Akebono marsh
Tsuchiyu-onsen
Fukushima, 2005
S. mytilus
97 μm
posterior rounded
Saitama, 1999
S. mytilus
144-200 μm
posterior pointed
Japan, 1998
S. mytilus
153 x 63 μm
posterior pointed
Japan, 1998
S. mytilus
μm
posterior pointed
USA, 1998
S. mytilus
110 x 46 μm
Kiyasse-Hanyu
Hanyu
Saitama, 2006
S. mytilus ?
119 x 44 μm
posterior rounded
lateral short cirri
Japan, 1998
S. mytilus
145 x 55 μm
Koyama River
Honjo
Saitama, 2006