PROCEEDINGS ON THE UNITED STATES NATIONAL MUSEUM 



hy the 



SMITHSONIAN INSTITUTION 



U. S. NATIONAL MUSEUM 

 Vol. 99 Washington : 1949 No. 3245 



A EEVIEW OF THE COPEPOD GENUS PARANTHESSIUS 



CLAUS 



By Paul. L. Illg 



The problem of arriving at a natural classification of the copepods 

 has been in no small measure complicated by the repeated appearance 

 within the group of the parasitic and commensal habit. In the cyclo- 

 poids, two sections, the Poecilostoma and the Siphonostoma, have been 

 established and remain well differentiated on the basis of the special- 

 ization of mouth appendages correlated with parasitic and semipara- 

 sitic existence. Unfortunately for the systematist, these copepods 

 seem to exhibit the widest tolerance in the selection of hosts. From 

 the records, any phylum above the Protozoa which is represented to 

 any conspicuous degixe in the marine fauna is likely to appear in the 

 roster of hosts of cyclopoid symbionts. This diversity of occurrence, 

 in addition to small size, inconspicuous appearance, and remarkable 

 agility in eluding usual methods of capture, has resulted in a scattered 

 and fragmentary representation of this group in museum collections 

 and consequently in the literature on copepods. The most extensive 

 reports to date either have been surveys of the faunas of fairly limited 

 localities or have been compendia of the symbionts of some particular 

 category of host, with the emphasis of interest frequently tending 

 toward the host rather than toward the copepod. 



Probably a high degree of artificiality has been introduced into the 

 classification because of this history. One of the major groups of the 

 copepods is now found defined in numerous publications as an assem- 

 blage of parasites and commensals of ascidians. This reference is. of 

 course, to the Notodelphyoida, which in such broad interpretation 

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