PROTOZOA AND OTHER ANIMALS 957 



is renewed multiplication of the basal granules and torsion of the ciliary 

 lines, leading to the characteristics of the trophont. In the active phases 

 of most species there is a more or less rudimentary, ventrally placed 

 mouth, which is surrounded by a characteristic rosette; sometimes the 

 mouth and rosette are lacking. 



Almost all the apostomes occur on or in marine animals. Chatton and 

 Lwoff (1935) assigned to the genus Gymnodinioides three species from 

 fresh-water Crustacea, two of which were described by Penard (1922) 

 as Larvultna, commensals on Gammarus, the third by Miyashita (1933) 

 as Hyalospira, from Japanese shrimps. 



Among the apostomes are the only ciliates with heteroxenous cycles, 

 cycles that alternate as regularly as those in many Sporozoa, though there 

 is no obligatory sexuality. 



In one group of apostomes, the phoront occurs on copepods, fixed to 

 the integument; and excystation with subsequent development occurs, 

 normally when the host is wounded or is ingested by a predator. The 

 ciliates, however, do not remain long enough in the predator for it to 

 be regarded as a second host. The predators involved are mostly co- 

 elenterates. The hydroid Cladonema radiatum appears to be a very special 

 site for the trophont of Spirophrya subparasitica, the phoront of which 

 is fixed to the integument of the benthonic copepod Idya furcata. When 

 the copepod is ingested, Spirophrya excysts and grows rapidly in its 

 remains, accumulating fluid or tissue material in a central vacuole. The 

 trophont does not encyst within the predator, but is expelled with the 

 residues of digestion. Encystation takes place on the carcass of the cope- 

 pod, in the environment, or on the stalk of Cladonema, producing a 

 tomont. This divides into a number of tomites, which may live free for 

 a few days, and eventually degenerate or become fixed to Idya. The 

 phoronts of apostomes of this group will excyst when the copepod molts, 

 but subsequent development is not normal (see Kudo, 1939, Fig. 257). 



In a second group of apostomes there are encysted phoronts on Crus- 

 tacea, excystation occurs at the molt, and the trophonts develop in the 

 exuvial fluid. Species are associated with a great variety of Crustacea, 

 including Entomostraca, balanids, copepods, and many Malacostraca. 

 The widely distributed genus Gyjnnodmwides belongs in this group. 

 Polys p ha is another genus. P. del age 2 is phoretic on the gill leaves of 

 pagurids {Eupagurus bernhat'dus) . Excystation occurs at the molt, and 



