626 PROTOZOOLOGY 



Genus Ptychostomum Stein {Lada Vejdovsky). Sucker circular or 

 ovoid; macronucleus ovoid or reniform, not elongate; in oligochaetes. 

 Several species. 



P. hacteriophilum Miyashita (Fig. 294, e). Elongate oval; 70-130/i 

 by 30-45m; sucker oval and large, about SO/x in diameter; macronu- 

 cleus ellipsoid ; endoplasm with numerous rods (symbiotic bacteria?) ; 

 in Criodrilus sp. (Oligochaeta). 



Family 4 Ancistrumidae Issel 



Genus Ancistruma Strand {Ancistrum Maupas). Ovoid, pyriform 

 or somewhat irregular; flattened; right side with more numerous 

 large cilia than the left; peristome on right side; cytostome near 

 posterior extremity; macronucleus round or sausage-shape, central; 

 a micro nucleus; contractile vacuole posterior; commensal in the 

 mantle cavity of various marine mussels. Many species. 



A. mytili (Quennerstedt) (Figs. 18; 294,/, g). Oval; dorsal surface 

 convex, ventral surface concave; dorsal edge of peristome curves 

 around the cytostome; peristomal floor folded and protruding; 

 longitudinal ciliary rows on both surfaces; three rows of long cilia on 

 peristomal edges; macronucleus sausage-form; a compact micro- 

 nucleus anterior; 52-74/i by 20-38m. Kidder (1933) found it in abund- 

 ance in the mantle cavity of Mytilus edulis at Woods Hole and New 

 York. 



A. isseli Kahl (Fig. 294, h). Bluntly pointed at both ends; 70-88m 

 by 31-54/i. Kidder (1933) observed it abundantly in the mantle cav- 

 ity of the solitary mussel, Modiola modiolus, Massachusetts and 

 New York, and studied its conjugation and nuclear reorganization. 



Genus Eupoterion MacLennan and Connell. Small ovoid ; slightly 

 compressed; cilia short, in longitudinal rows; rows of long cilia in 

 peristome on mid-ventral surface and extend posteriorly, making a 

 half turn to left around cytostome; small conical cytostome lies in 

 postero-ventral margin of body; contractile vacuole terminal; large 

 round macronucleus anterior; a micro nucleus; commensal. 



E. pernix M. and C. (Fig. 295, a). 46-48 ciliary rows; 6 rows of 

 heavy peristomal cilia; 38-56m long; in the intestinal contents of the 

 mask limpet, Acmaea persona; California. 



Genus Ancistrina Cheissin. Ovoid; anterior end attenuated; peri- 

 stomal field along narrow right side; 15-18 ciliary rows parallel to 

 peristomal ridges; cytostome right-posterior, marked with oral ring, 

 with a membrane and a zone of membranellae; right ridge of peri- 

 stome marked by two adoral ciliary rows; macronucleus anterior, 

 spheroidal; a micro nucleus; commensal. 



