BRACHIOPODA 



49 



The shell is only partially filled by the body, and the valves are lined 

 by the mantle lobes, whose free edges are bristled. The mantle lobes 

 enclose a large mantle ca\'ity. In the body is a spacious coelom, which is 

 extended into the mantle lobes. The coelom contains the digestive tract, 

 the liver, and the reproductive organs. The latter are chiefly in the 

 mantle lobes. The digestive tract, which is bent much as in the Polyzoa, 

 consists of gullet, stomach, and intestine. The mouth is surrounded by the 

 tentacled lophophore or " arms." The inner surface of the tentacles is 

 covered with cilia, which set up currents in the water and sweep minute 

 animals and algae into the mouth for food. The heart, usually present, lies 



Fig. 38. — Diagram of a brachiopod: b, Tentacles around mouth, m; i, 

 intestine; the shell black, the stalk to the right. (Kingsley's "Compara- 

 tive Zoology," Henry Holt & Co., Publishers.) 



dorsal to the stomach, to which it is attached. The nervous system con- 

 sists of an esophageal ring. Sense organs are usually wanting in the 

 adult. 



Important Biologic Facts. — For the first time, according to 

 the classification used, a closed system of blood-vessels and 

 red blood-corpuscles are found. 



The digestive tract has been developed into gullet, stomach, 

 and intestine, and a liver also appears. 



The Brachiopoda were formerly supposed to belong to branch 

 Mollusca. But the valves of the shell are dorsal and ventral, 

 not right and left, while the tentacled lophophore, the character 

 of the nephridia, and the modified trochosphere larva all tend 

 to show relationship with members of branch Molluscoida. 



Classification. — 



Class. 

 I. Polyzo'a. 



II. Phoroni'da. 

 III. Brachi6p'oda. 

 4 



Example. 

 Bugula avicularia (Bird's-head 



Coralline) . 

 Phoronis. 

 Magellania. 



