CHAPTER IV 



THE COPEPODA 



SUB-CLASS COPEPODA, H. Milne-Edwards (1830). 



Order 1. Eucopepoda. 



Sub-Order 1. Gymnoplea. 



Tribe 1. Amphaskandria. 



2. Heterarthrandria. 

 Sub-Order 2. Podoplea. 



Tribe 1. Isokerandria. 



2. Ampharthrandria. 

 Order 2. Branchiura. 



Definition. Crustacea in which there is no distinct shell-fold, 

 though the dorsal shield of the cephalon may be enlarged by the 

 coalescence of one or more of the trunk-somites ; there are typically 

 nine free trunk-somites (besides the telson), the last four without 

 appendages ; the telson bears a caudal furca ; the antennules and 

 antennae are generally large, the latter sometimes biramous, 

 and both may be used for locomotion or for prehension ; the 

 mandibles may have a palp, sometimes biramous ; there are 

 typically six pairs of trunk -limbs, the last five biramous and 

 natatory, but the sixth pair are frequently reduced or absent ; the 

 genital apertures are on the seventh trunk -somite (except in 

 Branchiura) ; the paired eyes are absent (except in Branchiura) ; 

 development with metamorphosis, the young generally hatched in 

 nauplius stage. (Most of these characters are subject to modifica- 

 tion in parasitic forms.) 



Historical. The relatively large size attained by some of the 

 parasitic Copepoda renders it probable that they were the first to 

 attract attention, and it is possible, though not certain, that they 

 are referred to in certain passages of Aristotle. The minute free- 

 living forms remained unnoticed till some of the microscopists of 

 the seventeenth century notably Leeuwenhoek described and 

 figured the common freshwater Cyclops. It was long, however, 



71 



