Tetrodontidae ; 



Sphaeroides annulatus (Jen. ). 



S, maculatus (Bloch et Schneid. ). 



Diodontidae: 



Diodon hystrix L. 



Thus we see that in natural conditions this species is en- p. 225 



countered only on the perch-bass family (Perciformes, nobis) and basically 

 on Chaetodontidae. In aquarium conditions, i.e., in relatively crowded 

 conditions, 48 more species are infected in addition to the above -noted 

 nine species of the perciformes type. These are related to 17 families of 

 three orders of fishes. In the opinion of the majority of the ichthyologists, 

 the relation between these orders is undoubtedly consanguinous. Thus, 

 Nikolsky (1954) writes that, "there are many bases for considering 

 Beryciformes as a group which is initial (hereditarily ancestral, nobis) 

 for the perca-type (Perciformes, nobis). " In the system of fishes of L. 

 C. Berg (1940) it is indicated that Tetrodontiformes are connected through 

 Acanthuridae with the Perciformes. In the scheme of phylogenetic relations 

 of bony fishes in the work of Gregory (Gregory, 1951) the connections be- 

 tween all three orders (Berycoidei, Acanthopterygii, in the narrow sense, 

 and Plectognathi- -according to the terminology of Gregory) are fully 

 apparent. Thus, contrary to the two preceding cases and in spite of the 

 huge number of hosts, B. melleni nevertheless parasitizes (only, nobis) 

 more or less related groups of fishes. This circumstance is especially 

 indicated by the fact that in the New York Aquarium, where together with 

 the infected fishes , others were kept as well, Elasmobranchii (sharks as 

 well as skates) were never infected, and among Teleostomi--the repre- 

 sentatives of Anguilliformes (Muraenidae), Cyprinodontiformes (Poeciliidae), 

 Syngnathiformes (Syngnathidae), Echeneiformes (Echeneidae), and 

 Batrachoidiformes (Batrachoididae) were never infected. 



Tristoma coccineum is indicated from the perciformids, 

 Xiphias gladius L. (Xiphiidae), and Tetrapturus belone Raf. (Histiophoridae), 

 for the shark Sphyrna zygaena (L. ) (Sphyrnidae) and for Moonfish (Ocean 

 Sunfish, nobis) (Molidae, Tetrodontiformes). It is difficult to say anything 

 precise on the subject of the occurrence of this species; however, we 

 suppose that indications to its finding on the Moonfish pertain not to this 

 species but to Tristoma papillosum Diesing. The majority of the con- 

 temporary authors identify the latter type with Tr. coccineum which is 

 hardly justifiable (Sproston, 1946). Thus, it is more probable that the 

 given species is encountered only in the two closely related families 

 Xiphiidae and Histiophoridae and the comoletely unrelated family Sphyrnidae. 



oGlC/1^ X 



247 



