COPEPODA 755 



(in distinction from many of the Phyllopoda) , with four or five 

 two-branched swimming feet on the thorax and an abdomen with- 

 out appendages. The Copepoda are divided into two suborders, 

 the Eucopepoda and the Branchiura. 



The Eucopepoda do not have compound eyes, and the eggs 

 develop in one or two brood pouches or ovisacs attached to the 

 abdomen. The Branchiura have two compound eyes. The females 

 do not have ovisacs, but the eggs are laid on stones or other con- 

 venient hard surfaces. The Lody is flattened. The Eucopepoda 

 may be considered in two divisions, Gnathostomata, and Parasita 

 or Siphonostomata. The Gnathostomata include the free-swim- 

 ming Copepoda; they have appendages about the mouth adapted 

 to mastication and the full number of body segments. The Si- 

 phonostomata are parasitic; they have the appendages about the 

 mouth adapted for piercing or sucking, and generally also a re- 

 duced number of body segments. The following table shows this 

 classification : 



Branch: Arthropoda. 



Class: Crustacea. 



Subclass: Entomostraca. 

 Order: Copepoda. 



Suborder: (a) Eucopepoda. 

 Group i. Gnathostomata. 

 Group 2. Siphonostomata. 

 Suborder: (6) Branchiura. 



KEY TO NORTH AMERICAN FREE-SWIMMING COPEPODA 

 (GNATHOSTOMATA) 



1 (104) Cephalothorax and abdomen distinctly separated 2 



2 (76) Antennae long, commonly nearly or quite as long as the whole 



animal, and composed of 23, 24, or 25 segments. Antennae 

 of male asymmetrical, the right geniculate and modified as 

 a grasping organ. The fifth feet are unlike in the two sexes, 

 and in the male the right and left fifth feet are dissimilar. 



Family CENTROPAGIDAE . . 3 



3 (8, 73) Endopodites of first swimming feet composed of one segment. . 4 



4 (7) Endopodites of second, third, and fourth swimming feet composed 



of one segment. Each furcal ramus armed with three 

 large setae. Abdomen of male asymmetrical, and armed 

 on right side with a peculiar grasping arrangement. 



Epischura . . 5 



