^^^^ THE NEW EVOLUTION "^^"^ 



types. Other animal types which we commonly re- 

 gard as characteristic of the sea, as the coelenterates 

 (figs. 69-73, p. 117; figs. 75-80, p. 143), the polyzoans 

 (figs. 67-68, p. iii)and thenemerteans, are represented 

 in fresh water. 



It is worthy of special note that of the phyla or 

 major groups of animals no less than ten are exclu- 

 sively marine, having no representatives either on the 

 land or in fresh water. Of these ten major groups 

 seven are each composed of a very small number of 

 related and very similar species and play a wholly in- 

 significant part in the economy of the sea. These 

 seven groups which are structurally and anatomically 

 of the greatest interest, but otherwise of no impor- 

 tance, are the priapulids, the sipunculids, the pho- 

 ronids, the chastognaths or arrow- worms (fig. 6i, 

 p. Ill), thebalanoglossids, thecephalodiscids,andthe 

 cephalochordates. All are bottom livers except the 

 chastognaths, which live suspended in the water from 

 the surface down to a considerable depth. Except 

 for a single cha^tognath, none of these are known to 

 have any fossil representatives. But this means little, 

 as all are soft bodied creatures whose preservation in the 

 fossil state could result only from the merest accident. 



Another group which is exclusively marine includes 

 the brachiopods or lamp-shells (fig. 60, p. iii). They 

 live on the bottom attached to rocks or other solid 

 objects, or burrowing in mud. There are less than 

 two hundred different kinds of brachiopods in the 

 present seas; but in the distant past they were vastly 

 more numerous and important. 



