PELAGIC FLOATING CRUSTACEA 141 



altogether absent. Associated with them we find 

 one or two species of Cladocera, a larger number of 

 Ostracoda (chiefly of the family Halocypridae), a few 

 Mysidacea, the Amphipoda of the suborder Hyperi- 

 idea, the Euphausiacea, and some of the shrimp- 

 like Decapods ; while the larval stages of these and 

 other groups also form an important part of the 

 plankton. 



It is necessary to make a distinction between the 

 " neritic " plankton of shallow water near the coast 

 and the " oceanic " plankton of the open sea. In 

 the inshore waters the plankton consists not only of 

 organisms that pass the whole of their life at or near 

 the surface, but also, and very largely, of the free- 

 swimming larvae of bottom-living species, and of 

 others that make occasional and temporary excur- 

 sions to the surface. For example, if the tow-net 

 be used a short distance from land — say in some 

 sheltered bay on our own coasts — the catch will 

 often be found to consist largely of larval Crustacea. 

 The zoea and megalopa stages of Crabs, the zoea 

 and schizopod stages of Prawns and Shrimps, are 

 often conspicuous by their numbers, or we may find 

 swarms of the nauplius and cypris larvse of Barnacles. 

 Sometimes, and especially at night, numbers of 

 Cumacea may be found in the tow-net ; and it is 

 noteworthy that these are usually males, which leave 

 the females burrowing in the mud at the bottom, 

 and swarm to the surface for a brief period of 



