CHAPTER XXXII 



ORDER 5 PERITRICHIDA STEIN 



THE PERITRICHIDA possess a much enlarged disc-like anterior 

 end which is conspicuously ciliated. The adoral zone is 

 a right-handed spiral unlike those of the other orders men- 

 tioned in the preceding pages. Aside from a few genera such 

 as Trichodinopsis and young free-swimming individuals of 

 the stalked forms, the general body surface Is not ciliated. 

 Both free-swimming and stalked forms occur. The latter pro- 

 duce colonial forms. A test occurs among the members of 

 Cothurnia. 



Asexual reproduction is by binary fission and sexual repro- 

 duction occurs commonly. The majority are free-living, often 

 attached to various aquatic animals and plants, although a 

 few are parasitic. 



The order is here divided into four families: 



Without stalk; body barrel-shaped Family 1 Trichodinidae 



With stalk; body more or less conical 

 Peristome not spirally rolled 



Free-living attached forms; posterior end inflexible . Family 2 Vorticellidae 



Attached; posterior end flexible Family 3 Licnophoridae 



Peristome spiral; sessil, with or without stalk. . . .Family 4 Spirochonidae 



Family 1 Trichodinidae Claus 



Genus Trichodina Ehrenberg. Body barrel-shape with a 

 row of posterior cilia. Posterior end forms a sucking disc. 

 Adoral zone at the anterior end. Nucleus band-form ; a contrac- 

 tile vacuole. All ectoparasitic. 



Trichodina pedicidus Ehrenberg (Fig. 169, a). On Hydra, 

 tadpole, etc. Body diameter 55 to 70 microns. 



Trichodina sp. Diller. On the skin and gills of the tadpoles 

 of Rana and Bufo. Body 30 to 40 microns in diameter. 



Trichodina asterisci Gruber. On starfish. 



Genus Cyclochaeta Jackson. Body on the whole similar to 



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