200 ANIMALS OF THE SEASHORE 



average collector, or if seen the species are very 

 difficult to determine. Therefore they are not 

 treated in this book. 



Other minute Crustacea often obtained by a tow 

 net, which are not discussed in this book, are the 

 Cladocera (Water fleas), Ostracoda and Cumacea. 



CIRRIPEDIA 



(Barnacles) 



Barnacles were for a long time classified with 

 the Mollusca (shell-fish) and it was not until their 

 life history was studied that their position within 

 the group Crustacea was fully recognized. 



When young, the barnacle is a minute free- 

 swimming animal with one eye, three pairs of legs 

 and a single shell. It grows and moults in the 

 manner of an insect until it has two eyes, six pairs 

 of legs and two shells. Then it attaches itself to 

 some solid object and completely changes its ap- 

 pearance. The bivalve shell disappears and it 

 develops a new shell made up of various plates. The 

 legs become modified to "cirripeds" — meaning 

 curled legs — giving the name to the order. These 

 legs are feather-like and, when extended, are con- 

 stantly waving, thus creating a current which carries 

 food to the mouth of the barnacle. These legs are 

 withdrawn within the shell when the animal is 

 disturbed. 



Some barnacles are sessile, attaching themselves 

 directly to some solid object; others are stalked. 

 Many barnacles attach themselves to ships and often 

 occur in such great numbers as seriously to diminish 

 the speed of the vessel. 



