SPIROTRICHA, HETEROTRICHA 



637 



Peristome at posterior end; cyto pharynx directed anteriorly 



Family 7 Clevelandellidae (p. 648) 



Body ciliation either confined to ventral side or lacking 



Free-living; flattened; cilia only on ventral surface; adoral zone sur- 

 rounds anterior region of ventral surface; cytostome on left edge 

 near the middle of body Family 8 Peritromidae (p. 649) 



Ectocommensal; extremities discoid; body narrowed; anterior disk 

 surrounded spirally by adoral zone; posterior disk bears mem- 

 branous cilia Family 9 Licnophoridae (p. 649) 



Family 1 Bursariidae Perty 



Genus Bursaria Mliller. Ovoid; anterior end truncate, posterior 

 end broadly rounded; dorsal surface convex, ventral surface flat- 

 tened; deep peristome begins at anterior end and reaches about 



Fig. 300. a, Bursaria truncatella, X60 (Kahl); b, Thylacidium trunca- 

 tum, X440 (Schewiakoff ) ; c, Bursaridium difficile, X210 (Kahl); d, 

 Balantidium duodeni, X170 (Stein); e, B. praenucleatum, X950 (Kudo 

 and Meglitsch). 



central part of body, where it gives rise to cytostome and cyto- 

 pharynx, which is bent to left; lengthwise fold divides peristome into 

 2 chambers; striation longitudinal; ciliation complete and uniform; 

 macro nucleus band-form; several micronuclei; many contractile 

 vacuoles distributed along lateral and posterior borders; cysts with 

 a double envelope; fresh water. One species. 



