354 



Descriptive Zoology. 



The Polyzoa. These are chiefly, though not entirely, ma- 

 rine and are known as the "sea mats" or "corallines." 

 They are also known as the "moss animals." These 

 names come from the fact -that they grow in colonies like 

 mosses. They often incrust rocks with their skeletons, 

 which are either gelatinous, chitinous, or calcareous. 

 Each individual is frequently contained in a sort of cup, 

 into which it can retract or from which it can protrude to 

 a certain extent. There is a row of tentacles around the 

 mouth. One of our fresh-water forms (Pectinatella) has a 

 gelatinous basis or common body, which is found in spher- 

 ical masses as large as a man's head, 

 being attached to branches in the water. 

 The living animals are on the outside. 

 Such masses are often called "sponges" 

 by the fishermen. 



The Brachiopods. These are in- 

 closed in a bivalve shell, and are named 

 the " lamp shells." Their resemblance 

 to mollusks is very superficial, the 

 FIG. 201. LAMP SHELLS internal structure of the two being 

 totally unlike. There is usually a 

 circle of tentacles somewhat as in the Polyzoa. The 

 brachiopods are exclusively marine. They are attached 

 by a stalk which extends through the larger valve near the 

 hinge. There are many fossil brachiopods. 



