PROTOZOA AND OTHER ANIMALS 917. 



instead of eggs. Only the female hosts are able to propagate the infec- 

 tion. Codreanu (1934) remarked that this is the only sufficiently de- 

 fined case of true parasitism of the schizocoele of insects by ciliates. The 

 species found in Baetis by Lichtenstein was named by him O. collini; that 

 studied in Baetis by Codreanu (1930) was, he stated, probably the 

 same. 



Haas (1933) noted the similarity between the oral apparatus of the 

 swarmers of Ichthyophthirius multifliis Fouq. and that of Ophryoglena; 

 Kahl (1935), in consequence, placed that important parasite of fish in 

 the family Ophryoglenidae. Commensalism and parasitism being so well 

 developed in Ophryoglena, although along with free-living habits, there 

 are clear ethological relationships between it and Ichthyophthirius. 



Pleuronema anodontae, the only commensal species of that genus, was 

 reported by Kahl (1926) in small crushed mussels. He stated later 

 (1931) that it is infrequent in Anodonta, but occurs regularly in Sphae- 

 rium species. (Perhaps one should investigate the possibility that this 

 may be one of the Ancistrumidae, not Pleuronema.) Very close to 

 Pleuronema is Pleurocoptes hydractiniae Wallengren, an ectocommensal 

 on the hydromedusan Hydractinia echinata. 



Distributional Host Relationships and Host-Specificity 

 IN Representative Symbiotic Faunules 



GENERAL CONSIDERATIONS 



There are some generic groups of Protozoa that have a rather wide 

 distribution among animals; these groups are represented by species in 

 hosts widely separated systematically. That is true, for instance, of Hex- 

 amita and Trichomonas among polymastigotes, of Endolimax among 

 endamoebae, of Nosema and Eimeria among sporozoa, of Nyctotherus, 

 Balantidium, and urceolarids among ciliates. These examples have been 

 discussed by Wenrich (1935). The genus Trypanosoma is represented 

 in a very large number of vertebrates of all classes, but is limited to them, 

 as is also Giardia. (The occurrence of Giardia in nematodes is faculta- 

 tive; see p. 902.) A more or less closely restricted host distribution is, 

 however, characteristic of many generic, familial, and even higher groups 

 of Protozoa. Entodiniomorphina occur only in certain herbivorous mam- 

 mals, chiefly ruminants and Equidae; opalinids are most likely to have 

 anurous amphibian hosts, although a few have been found in Urodeles, 



