CHAPTER II 

 BIOLOGY OF MONOGENETIC TREMATODES 



The locations of monogenetic trematodes are quite diversified. p. 74 



As is known, they parasitize mainly sharks, skates, holocephalans and 

 bony fishes, amphibians and reptiles, and in addition, parasitic isopods, 

 and are also known to exist on cephalopods and aquatic mammals. 



The parasites of fishes are found on the gills, in the gill chamber 

 ajid buccal cavity, on the surface of the body, on the fins, in the cloacal 

 cavity and in its vicinity, in the ureters and the body cavity, and finally, as 

 an exception, in the heart. The majority of monogenetic trematodes para- 

 sitize the gills and may be located very differently thereon. A majority of 

 the species occur on the gill filaments, a few species of Gyrodactylus are 

 located on the gill rakers, and a number of Monocotylidae and Capsalidae on 

 the lateral surfaces of the gill arches, mainly on Elasmobranchii. 



The parasites which occur on the gill filaments are distributed 

 differently. First of all, many forms occur on all four gill arches of the 

 fishes and five to seven arches of the shark-types whereas others locate on 

 the second and third arches in most cases or even exclusively. Thus, as 

 a rule, a number of species of Mazocraeidae do not occur on the fourth arch 

 and very seldom occur on the first, even in the case of relatively high levels 

 of infection. Different species have favored places of location within the 

 limits of a single gill arch. Some species (many Dactylogyridae and others) 

 are located along its entire length, while others are either located only in 

 the middle (for instance Diplozoon), or at either end (on the anterior end, 

 for instance Monocotyle and the posterior, Nitzschia). Likewise the lo- 

 cation in relation to the length of the gill filaments varies among different 

 species. Thus, as a rule, Dactylogyrus anchoratus Dujardin settles at the 

 base of the gill filament, whereas Dactylogyrus vastator Nybelin, on the 

 other hand, settles at their very tips. Very often "concomitant" (ternns of 

 V. A. Dogiel) species of Diplectanidae, Mazocraeidae and others can be 

 easily distinguished by their location on the gill filaments. 



Monocotylidae and Capsalidae live mostly in the gill and buccal 

 cavities. Representatives of the genera Benedenia and Capsala and others 

 which live in the gill chamber usually are located on the interior surface of 

 the operculum near the posterior bases of the gill arches. The worms lo- 

 cate differently in the buccal cavity. Thus>for instance, Nitzchia sturionis 

 (Abildgaard) occur in the lips, the palate, the tongue and sometimes even 

 in the beginning of the esophagus, and certain Monocotylidae - -quite to the 

 contrary- -live only on the surface of the palate. 



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