24 



LIFE IN THE SEA 



[CH. 



mollusca, many of the starfishes and their allies, and 

 indeed most of the groups of invertebrata. All these 

 larval creatures form what we may call the transitory 

 plankton. They live drifting about in the sea for a 

 variable period of their lives, and then they settle 



Fig. 3. Plankton. 1 and 2, pelagic worms; 3, a Medusa; 4, a 

 Copepod ; 5, a Ctenophore. All magnified. 



down to their final habitat as members of either the 

 Benthos or the Nekton. (2) The second and larger 

 part of the plankton consists of organisms which live 

 there permanently. 



