522 ZOOLOGY SECT. 



ORDER 3. COPEPODA. 



Entomostraca, mostly of small size, having an elongated body 

 distinctly segmented except in certain parasitic forms. The 

 carapace may extend over the first thoracic segment. The thorax 

 bears, in the free forms, four or five pairs of biramous appendages : 

 the abdomen is limbless. Many species are parasitic, and show 

 various stages of degeneration of structure. 



Sub-Order a. Eucop&podc < . 



Free or ectoparasitic Copepoda having biramous swimming-feet 

 and biting jaws, or, in the case of parasitic forms, a more or less 

 degenerate structure, and jaws often adapted for sucking. The eggs 

 undergo development in paired brood-pouches attached at the base 

 of the abdomen. 



In this group are included (a) free-swimming forms, such as 

 Cyclops (Water-flea), and (/3) parasitic forms, or Fish-lice e.g. 

 Ergasilus, Choncfracanthus, Lerncea (Figs. 416 and 417). 



Sub-order b. Branchiu ra. 



Ectoparasitic Copepoda having compound eyes and a suctorial 

 mouth. The second maxillse form sucking-discs for attachment to 

 the host. The whole body is strongly depressed, and there are no 

 brood-sacs. 



Including the carp-lice, Argulus (Fig. 418). 



ORDER 4. CIRRIPEDIA. 



Imperfectly segmented marine Entomostraca, often of con- 

 siderable size, and either fixed during adult life or parasitic. 

 The sexes are united, and the sperms are motile. 



Sub-order a. Eucirripedia. 



Fixed or parasitic Cirripedia in which the body is usually 

 enclosed in a fold of skin, strengthened by calcareous plates. The 

 abdomen is rudimentary. There are usually six pairs of biramous 

 appendages. 



This group includes (a) fixed forms, such as Lepas (Barnacle) 

 and B<d<ii(nx (Acorn-shell), and (#) parasites e.g. Pet /-area, Al- 

 <-ippe, Proteolepas (Figs. 419 and 420). 



Sub-order b. Ehizoccphala. 



Parasitic Cirripedia in which the body has undergone extreme 

 degeneration, having no trace of segmentation or of appendages in 

 the adult condition. The juices of the host are absorbed through 

 long root-like processes. 



Including Sacculina and Peltogastcr (Fig. 421). 



