WORMS. 247 



ORDER II. BRACHIOPODA (Lamp shells). 



From the fact that the Brachiopoda possess a bivalve 

 shell, these forms were formerly included among the 

 molluscs near the clams. A little examination, however, 

 shows that the resemblance between them is but slight. 

 The two valves of the Brachiopod are unequal in size, and 

 are dorsal and ventral, rather than right and left, as in the 

 clams. Near the point where the two parts (valves) are 



FIG. 117. Diagram of a Brachiopod. b, tentacles around mouth, m ; i, in- 

 testine ; the shell black, the stalk to the right. 



hinged together there is usually an opening * in the larger 

 valve through which a fleshy peduncle or stalk projects, by 

 means of which the animal is fastened to some support. 

 Inside the valves, which can be closed by muscles, are the 

 principal organs. Near the mouth are found a number of 

 delicate tentacles (much like those of the Polyzoa), the disk 

 which bears them being frequently rolled into a spiral. 

 The alimentary canal is bent, but a vent is occasionally 

 lacking. 



The Brachiopods are all marine. There are few in 

 existing seas; but they are among the oldest inhabitants, 

 for the shells are found fossil in all rocks from the oldest 

 down to the present time. 



* In some the peduncle extends from between the valves instead of 

 having a special opening. 



