Parasites of migratory and fresh water fishes (Salmonidae, 

 Thymallidae, Cyprinidae, Catostomidae and Cobitidae. 



Palombi. 



p. 424 

 The family is divided into Discocotylinae Price, and Diplozooninae 



The present family, in the scope accepted by us, comprises 

 only part of thespecles ascribed to it by Price (Price, 1936) and Sproston 

 (Sproston, 1946) and parasitizes practically only fresh water fishes. 



Q.1MM 



Fig. 300. Discocotyle sagittata (Leuckart), chitinous parts of the attaching 

 clamp. A- -An artificially unfolded view; B--In normal condition. 



In addition to the structure of the adult animals, the presence 

 of larvae which possess still another pair of fully developed clamps capable 

 of immediate attachment in addition to the hooked, partially reduced 

 (Diplozoon) armature is characteristic for these species. This peculiarity 

 among fornns bearing 4 pairs of clamps in the adult state is encountered 

 only among representatives of the present family and generally- -only on the 

 highly specialized Microcotylidae. Also important is the circumstance that 

 in the larva of Discocotylidae there is one pair of middle hooks which re- 

 inains without changes in the adults, in contrast to the majority of 8-clamped 

 forms among which one or more pairs of middle hooks appear, as a rule, 

 either during the embryonic or posteinbryonic period. Similar relations 

 are observed among Mazocraeidae, Plectanocotylidae, Anthocotylidae, 

 Hexostonnatidae and even among such a remote family from the families 

 enumerated as Chimaericolidae. Only Diclidophoridae have one pair of 

 middle hooks in the adult state just as the Discocotylidae (certain 

 Diclidophoridae apparently loose their nniddle hooks in the postembryonic 

 period--see page 431), but their larvae are easily distinguished by the 

 absence of the clamps^ whereas the adults--by a nunnber of anatamo- 

 morphological characteristics (see pages 431 - 438). 



508 



