164 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 112 



used (Humes, 1949, 1957) in characterizing the species of Clausidium, 

 a genus belonging to the same family, and the ecological differences are 

 much greater; also with respect to adhaerens and arenicolae, there is 

 some evidence for sympatry, although no intermediates occurred 

 among the specimens that I have examined. 



This superspecies would be characterized mainly by the separation 

 between genital and first abdominal segments and the well-developed 

 sixth legs in the adult females; the reduced mandibular setation 

 and presence only of simple terminal elements on the maxilla and 

 of setulose exopod spines on all the swimming legs in both sexes; and 

 the attenuated "scaly'' tip of the male maxilliped. Its members are 

 known only from the New World but appear morphologically quite 

 similar to the species of Giardella that have been reported from the 

 coasts of France and England. 



The species discussed range from forms found free-living {adhaerens) 

 to those which, under natural conditions, seem to remain in contact 

 with their hosts (thysanotus and elongatusl). Intermediate between 

 these extremes are associates which may inhabit the burrow but 

 seldom stray onto the body of the host (subadhaerens) , or apparently 

 are equally common in the one as on the other (arenicolae). Further 

 work is needed to determine whether species of the first type are 

 really independent and, for forms associated with other animals, 

 what are the relations of copepod and host. 



A feature of the species thysanotus and subadhaerens (the only ones 

 examined alive) is the presence, mainly in the prosome, of droplets of 

 a red, oily-appearing material among the organs. It appears to be 

 incorporated in the eggs, and to a lesser extent the spermatophores, 

 and occurs in the nauplii. Such stored material is very characteristic 

 of species of Clausidium,, which are also associated with Callianassa. 

 It is responsible for the bright red color of these copepods. Its presence 

 seems not to depend on an association with callianassids, however, for 

 Sars (1917) described a female of the apparently free-living Hemi- 

 cyclops purpureus as having "bright red" ovarial tubes and ovisacs. 

 These observations are consistent with what is known about carotenoid 

 metabolism in copepods and other Crustacea and, if chemically of 

 this nature, the substance probably has its origin in the organism's 

 food (Fox, 1953). Thus, in species associated with Callianassa, it 

 could presumably be derived from plant and/or bacterial matter, from 

 the host's blood, or from the eggs of berried female mud shrimp. 



The key below refers to the presently known species of Hemi- 

 cy clops that I have examined from North and South America. It is 

 applicable to the adults of both sexes but will probably also serve to 

 distinguish immature specimens, at least to morphological group. 

 The structure of the maxillipeds and the nature and position of the 



