A NEW GENUS OF TREMATODES FROM THE WHITE 



BASS. 



J^y H. J. Van Cleave, 



Of the University of Illinois, Urbana, Illinois. 



INTRODUCTION. 



DiiriiifT the summer of 1919, the writer was engaged in investi- 

 gations for the United States Bureau of Fisheries upon worm para- 

 sites in fishes of the Mississippi River and some of its tributary 

 streams and lakes. Collections were made in Iowa, Hlinois, and 

 Minnesota. In the course of this w^ork some unusual trematodes 

 were encountered in the digestive tract of the white bass, Roccus 

 chrysops (Rafinesque). These, in some superficial respects, re- 

 semble members of the genus Acanthochasmus of Looss, but the in- 

 ternal organization differs so pronouncedly from that of any recog- 

 nized species of Acanthoclid.wius that it becomes necessary to erect 

 a new genus for which the name Allacanthochasmus is proposed. 



Looss (1899:579) has aptly shown that superficial resemblances 

 are not sound criteria for the determination of phylogenetic rela- 

 tionships between trematode genera when he pointed ©ut the essen- 

 tial differences between the two genera Acanthochasmus and Ste- 

 phanochasmus. In like manner he called attention to the funda- 

 mental differences which exist between these two genera and the 

 genus Ech'mostomum even though all three of these genera display 

 a pronounced crown of oral spines. The presence of conspicuous 

 spines around the oral orifice, though a conspicuous character, is 

 in itself of little or no phylogenetic significance. Accepting this 

 same fundamental hypothesis, Odhner (1911:522) has maintained 

 that the two genera Caecincola and Cryptogonimus are closely re- 

 lated to the genus Acanthochnsmus in spite of the fact that in them 

 oral spines are lacking. On the other hand, in comparing the trem- 

 atodes from the white bass with others having the oral crown of 

 spines, unique conditions in the relative position of testes, ovary, 

 and uterus and numerous other differences of fundamental im- 

 portance are encountered. 



This paper forms one of the contributions from the United States 

 Bureau of Fisheries Biological Station, Fairport, Iowa, and from 

 the Zoological Laboratory of the University of Illinois, No. 194. 



No. 2430— Proceedings U. S. National Museum. Vol. 61, Art. 9. 



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