PHYLUM PRYOZOA 191 



molluscs when there were no vertebrates to interfere with 

 their simple activities. 



PHYLUM BRYOZOA 



Bryozoans, or "moss-animals" are usually colonial in 

 habit and resemble hydroids in general appearance. Most 

 species are marine but a few occur in fresh water. They 

 appear as encrustations, or as little- plant-like growths, 

 attached to objects in the water. The individuals of a 

 colony are called zooids. Each has a circle of tentacles 

 about the mouth and shows a superficial radial symmetry, 

 as is the case in many attached animals. The digestive 

 tube is U-shaped and the anus therefore opens near the 

 mouth. Despite their superficial resemblance to hydroids, 

 bryozoans are more nearly related to the worms. They, 

 like the brachiopods, are peculiar on account of their seden- 

 tary existence. 



