AILMENTS AND DISEASES 



FIG. 96 



Trichoditia pediculus 



a Hirudinld parasite. 



Greatly enlarged. 



its host; and produces tiny red external, gill and throat 

 ulcers into which it is pitted like a cancer. When present 

 in numbers it is a dangerous parasite and has been found 

 on fishes afflicted with what is popularly known as Twitters. 

 It has a nearly circular ciliated body and on its lower side a 

 suctoral disc. 



Arachnia or Arachnid Parasites. This group 

 includes the Mites, Ticks, etc., of which some of the aquatic 



species are discussed in the appendix to the Aquatic Insects. One family, 



Trachearia, contains strictly parasitic genera, and the 



Acharidie and Hydrachnida have parasitic and predatory 



members which subsist largely on the freshwater fauna. 



The common form is the red Water-mite, Hydrachna 



geographica. Fig. 97. With five other families of this 



group parasitism is but slight and on the higher 



Vertebrates. 



Crustacea or Crustacean Parasites. This 



group includes the so-called Fish Lice, small crustaceans known as Epizoa, 



and belonging to the families Lernieda, Caligidie and Argulida. 



Lern^d^ and Caligidie. The members of these families rarely 



occur as parasites on the freshwater fauna, having those of saltwater as 



hosts; but some are brought into freshwater by marine fishes in their 



FIG. 97. Hydrachna 



geographica, an Arachnid 



parasite. Enlarged. 



FIG. 98. Lerneecera 

 cyprinacea, a Crustacean 

 parasite. Adult and free- 

 swimming larva. Enlarged. 



FIG. 99. Lernacera cyprinacea, attached 

 to the gill of a young Large-mouthed Black 

 Bass. Slightly enlarged. 



spawning migrations. One form, Lernacera cyprinacea. Figs 98 and 99, 

 occurs in freshwater and is a frequent parasite on fishes. It attaches itself 

 by peculiar sucker-tentacles to the gills, fins and surface, and is a very fre- 

 quent parasite on river and pond fishes, of such size as to be easily seen. 

 Argulid^. These Copopods are known as Carp-lice, though they 

 have almost all the freshwater fishes and amphibia as hosts. Of the three 

 genera Argulus, Chonopeltis and Bolops, 42 species have been recognized, 



152 



