CLASS CRUSTACEA. 



SUB-CLASS ENTOMOSTRACA. 



Order COPE POD A. 

 Tribe I. CYCLOPOIDA G. 0. Sars. 



Cephalothorax ovate and usually more robust than 

 the abdomen. Antennules slender and elongated or 

 tolerably short and stout; those of the male alike on 

 both sides, sometimes modified for grasping. 



Antennae unbranched, or the outer branch rudimen- 

 tary ; usually feebly armed, but sometimes stout or 

 elongated and provided with strong terminal claws. 

 Maxillipeds usually less developed than in the Cala- 

 noida, but the second pair sometimes strongly uncinate. 



First four pairs of swimming legs as in the Cala- 

 noida ; fifth pair rudimentary, alike in both sexes, 

 usually one- but sometimes two- jointed, rarely with 

 more than two joints. Egg-strings two. 



The Cyclopoida found on British fishes all belong to the 

 one family Ergasilidae, and to the three genera Ergasilus, 

 Bomolochus, and Thersitina. The species comprised within 

 these three genera are associated with fishes of various kinds. 

 They cannot all be accurately described as parasites, some of 

 them, such as Bomolochiis soless, should rather be regarded as 

 commensals ^>r messmates ; they appear to be able, within 

 certain limits, to move about with considerable freedom. 

 Their food appears for the most part to consist of the mucus 

 exuded by the fish, and it is doubtful if they would long sur- 

 vive it' removed from their host. 



Family i. ERGASILIDAE. 



Body more or less cyclopoid in form. First segment 

 usually large, sometimes subglobose in the female. 

 Antennules composed of five to seven joints. Antennae 



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