PART II 



OCCURRENCE OF MONOGENETIC TREMATODES ON THEIR HOSTS 



CHAPTER I 



HOSTS OF MONOGENETIC TREMATODES 



As a rule monogenetic trematodes parasitize vertebrates. p^ 219 



Their discovery on cephalopods (Cephalopoda) and on isopods (Isopoda 

 parasitica) appears to be an exception. Until this time only one nnono- 

 typical genus Isancistrum Beauchamp (I. loliginis Beauchamp) from the 

 gills of Loligo vulgaris L. and L. media L,. , which was encountered only 

 once, is known. Those monogenetic trematodes parasitizing the Isopoda 

 parasitica are related to the family of Diclidophoridae. They arouse a 

 great interest because they indicate the possibility of a change toward 

 superparasitism. However, it seems to us that here we deal not so 

 much with the adaptation to a new group of hosts, a group strongly 

 isolated from the preceding ones (isopods --fishes), but rather we deal 

 with the adaptation to a new place of parasitizing on the same host, a 

 place which also became a new host. If we remember that until the 

 present time these parasites were found basically on the isopods living 

 in the bodies of fishes and never in the free-swimming ones, this point 

 of view will not appear paradoxical. 



Among the vertebrates, the hosts of monogenetic trematodes 

 appear to be mainly representatives of the three classes of fishes: 

 shark-types (Elasmobranchii), full -headed -typed (Holocephali), and the 

 highest fishes (Teleostomi), and to a much smaller degree on amphibians 

 (Amphibia) , and reptiles (Reptilia). As an exception one genus and 

 species from an aquatic mammal is known, specifically Oculotrema 

 hippopotami, described by Stunkard (Stunkard, 1924)^ from the eye of the 

 hippopotamus from Africa. One must note with this that it is possible 

 that the parasite was erroneously mistaken for a parasite parasitizing 

 (another one which normally parasitizes, nobis) the hippopotamus, for 

 judging by the work of Stunkard, the possibility of an error in labeling is not excluded^, and 

 by its structure O. hippopotami greatly resembles representatives of the 

 genus Polystomoides Ward and (species, nobis ) close to the latter. 



1 ■ 



In the work of Stunkard is indicated: "the material consists of 5 poly- 

 stomes which have the label 'from the eye of hippopotamus. ' It is 

 probable that they were collected by the late professor A. Loss from the 

 Nile hippopotamus from the Hij zoological garden in Cairo, Egypt, but 

 unfortunately, there was no other information (on the label, nobis)". 



239 



