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 



(BRACHIOPODS). ^^jjy un]ike There ig usuaUy 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. 



