PHYLUM MOLLUSCA 



283 



rare in very shallow water, and absent altogether from the littoral 

 zone ; some have been found at considerable depths (down to 1,250 

 fathoms). The Placophora are all vegetable feeders, their food 



cl.en 



neph 



cm 



FIG. 158. Chiton, nephridial and genital systems, an. anus ; cten. ctenidia ; 

 gen ap. genital aperture ; gon. gonad ; gono<i. gonoduct ; inc. mouth ; neph. ap. 

 nephridial aperture ; n. feri. ap. aperture from nephridia to pericardium. (From 

 Simroth, after Haller and Lang.) 



consisting of minute alga? and diatoms. The Aplacophora subsist 

 on small animals. The Placophora when at rest adhere firmly to 

 the surface of a rock or a block of coral by means of the sucker-like foot. 

 When forcibly detached the animal curls itself up into a ball, and 



