936 PROTOZOA AND OTHER ANIMALS 



In the family Thigmophryidae, Thigmophrya hivalviorum, which 

 occurs on the gills of the marine pelecypods MactYa solida and Tapes 

 pullastra, has a thigmotactic region reduced to an elliptical area in the 

 anterior fifth of the body (Chatton and Lwoff, 1923a). The movements 

 of the cilia of this area are not synchronous with those of the rest of 

 the body. The ciliate swims in the mantle cavity or fixes itself to the gills. 



The family Ancistrumidae is large and diverse. In general, the ciliates 

 are more sedentary than those previously considered in the order Thigmo- 

 tricha and the thigmotactic area is still more restricted. Although the 

 most frequent habitat is the mantle cavity of Pelecypoda, other molluscs 

 as well as members of other phyla of invertebrates serve as hosts for 

 species of the family. Probably, however, the original hosts were Pelecy- 

 poda. 



The two principal genera are Anchtruma Strand, 1928 (given incor- 

 rectly as 1926 by Kahl and Kidder) (Fig. 199B, C) and Boveria 

 Stevens, 1901, but there are many others: Eupoterion MacLennan and 

 Connell, Ancistrina Cheissin, Ancistrella Cheissin, Plagiospira Issel 

 (Fig. I99D), Ancistrospira Chatton and Lwoff, Proboveria Chatton and 

 Lwoff, Tiarella Cheissin, Hemispeira Fabre-Domergue (Fig. 200C), 

 Hemispeiropsis Konig (Fig. 200A, B). Kahl (1934) put into the fam- 

 ily, though doubtfully, two ciliates parasitic in Littorina, Protophrya 

 ovicola Kofoid and Isselina intermedia Cepede. 



The Ancistrumidae possess more or less conspicuous peristomal cilia; 

 often these rows constitute a prominent fringe. In typical forms the 

 organisms adhere to the surfaces on which they live by the thigmotactic 

 cilia in a tuft at the anterior end. Ancistrella choanomphthali, however, 

 adheres to the gills by its entire concave, ventral surface (Cheissin, 1931 ) • 

 In the Ancistrumidae an evolutionary series is apparent in the shifting 

 posteriorly of the mouth and of the peristome, which becomes spiraled. 

 Chatton and Lwoff (1936b) suggested that the Ancistrumidae constitute 

 so extraordinarily homogeneous a family that we may consider that there 

 is only one genus, subdivided into subgenera, an opinion that expresses 

 the homogeneity, though possibly the conclusion that there should be 

 only one genus is not sound taxonomically. These authors remarked that 

 the characteristics separating the genera or subgenera are purely quanti- 

 tative, consisting of more and more accentuated retrogradation of the 

 mouth and prostomal ciliary lines from the anterior half of the body 

 to the posterior end (Fig. 200K-N). 



