BRACHIOPODA 



177 



body, and may be coiled in a very complicated manner. 

 Rhynehonella the lophophore is 

 protrusible, but this is excep- 

 tional. 



The edges of the mantle 

 usually carry a row of setae, 

 which arise from ectodermal pits, 

 as in Chaetopods. 



The intestine in Zingula is of 

 some length, it takes one or two 

 twists, and terminates in an amis 

 which opens at the right side into 

 the mantle cavity between the 

 shells. In Discina also the anus 

 is lateral, but in Crania it opens 

 in the median line into a cavity 

 which lies between the posterior 

 ends of the valves where the 

 peduncle would normally be 

 found. 



The food of Brachiopods con- 

 sists chiefly of Diatoms and 

 minute unicellular Algae, which 

 are brought to the mouth by the 

 action of the cilia on the lopho- 

 phore. 



The only case of serial repeti- 

 tion of parts presented by the 

 Brachiopoda is the two pairs of 

 nephridia found in the genus 

 Bhynchonella. 



The sexes are separate in 

 Crania, but Zingula, and probably 

 some others, are hermaphrodite. 



The recent Brachiopods are 

 found in all seas, usually at 

 moderate depths, within 100 

 fathoms. Idngula and Glottidia 

 sometimes live between tide marks, but may extend to 



12 



In 



FlO. 113. — iMigvla anatina. Dia- 

 gram showing the muscular 

 system : after Hancock. 



1. Dorsal valve. 



2. Ventral valve. 



3. Peduncle. 



4. Heart. 



5. Alimentary canal. 



6. Anal aperture. 



7. Umbonal muscle. 



8. Central muscle. 



9. Transmedial muscle or sliding 

 muscle. 



10. Anterior muscle. 



11. Middle muscle. 



12. Adjusters, enabling valves to 

 move forward and backward on 

 each other. 



a 



