THE NORTH AMERICAN SEMIPARASITIC COPEPODS OF 

 THE GENUS CLAUSIDIUM. 



By Charles Branch Wilson, 



Of the Department of Biology, State Normal School, Westfield, Massachusetts. 



INTRODUCTION. 



There has been much discussion with reference to those copepods 

 which are found upon echinoderms, worms, mollusks, etc., as to 

 whether they were to be regarded as free-swimmers, semiparasites, or 

 true parasites. 



A number of closely related forms are constantly found in the 

 open ocean and are apparently genuine free-swimmers. And yet 

 even some of these, like Sapphirina, are known to infest various 

 pelagic animals at times. The fact that the parasitism is usually 

 temporary, the copepods easily changing hosts or moving about 

 freely in the water, is the disturbing element. There seems to be 

 an unwritten opinion that once a parasite always a parasite ought 

 to be the prevailing rule. 



And when we come to examine the mouth parts we find that they 

 are not suited either for mastication or for suction. They are rather 

 adapted for licking up nourishment from the surface of the various 

 organisms or from the walls of their inner (branchial) cavities. 



And yet Sars has shown in his Crustacea of Norway (vol. 6, p. 142) 

 that there is no doubt about the parasitic nature of these copepods. 



One of the more sedentary forms is the genus Clausidium, which 

 lives in the branchial cavity of certain Calianassa species. 



DESCRIPTIONS OF GENUS AND SPECIES. 



Genus CLAUSIDIUM Kossmann. 



Hersilia Philippi, Wiegmanna Archiv fur Naturgeschichte, vol. 5, 1839, p. 128. 

 Clausidium Kossmann, Verhandlungen clerphys.-med. GeseUschaft, n. s., vol. 7, 

 1875, p. 11. 



In 1839 Philippi established a new genus and species which he 

 named Hersilia apodiformis. Thirty-six years later Kossmann found 

 specimens of the same copepod and, not knowing Philippi's paper, 

 again made of them a new genus and species with the name Clausi- 

 dium testudo. 



Proceedings U. S. National Museum. Vol. 59- No. 2377. 



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