lOO 



THE CRUSTACEA 



ticidae, and Cyclopidae, are very abundant in fresh water. Most 

 of the Gymnoplea are pelagic, forming a very important part 

 of the plankton of the sea and of lakes. The non- parasitic 

 Podoplea, on the other hand, with the exception of a few pelagic 

 groups like the Corycaeidae, belong to the bottom-fauna. A large 



Newly hatched larva o'( Argnlus foliaceus. a', antennulo ; n", antPima ; nul, iiiaiiciililf ; njiH, 

 iiianclibular palp; m/', maxilla (lirst maxilliped) ; mf", (secondX-iiuixilliped ; j^, ;>■*, lirst and 

 fourth pairs of Kwiniming-ffet. (After Claus, from Korschelt aiidjHeider's liinlirnuloijy.) ■ 



proportion of the parasitic forms of various families attack fish, and 

 some of these, such as Lernaeocera and Achtheres, occur in fresh water. 

 Pennella is sometimes found on whales. Other parasitic and semi- 

 parasitic forms are found on various groups of marine inverte- 

 brates. The Branchiura are temporary parasites on fish and occur 

 both in the sea and in fresh water. 



Most of the free-living Eucopepoda are minute, but some of the 



