252 



COLLEGE ZOOLOGY 



(B, g) between the mantle (pa) and the foot (/). The mouth (tn) 

 is at one end and the anus (a) at the other. Examples: Ami- 

 cula, Trachydermon, Chiton. 



The chitons are slow-moving mollusks which live near the sea- 

 shore in shallow water. They are usually herbivorous. 



Order 2. Aplacophora. — These are worm-like mollusks 

 (Fig. 179, C) without a shell, but with many calcified spicules over 



A B 



Fig. 179. — Chitones. A, upper surface of Onithochiton. B, under sur- 

 face of Lepidopleurus. a, anus ; /, foot ; g, gills ; m, mouth ; pa, mantle ; 

 te, pallial tentacles. C, ventral view of Paramenia, b, mouth; si, foot groove. 

 (A from Tryon; B and C, from Lankester's Treatise.) 



the surface. The mantle surrounds the entire body, and the foot 

 lies in a groove (si). Example: Chatoderma. 



The Aplacophora live on coral polyps and hydroids. They 

 are most abundant at a depth of about fifty fathoms. 



3. Class II. Gastropoda 



The snails, slugs, limpets, and other similar mollusks belong- 

 ing to this class possess a foot, a mantle, and a mantle cavity 

 comparable with those of the mussel (Fig. 172, I— II) , but they 

 differ considerably in the form and structure of their bodies as 

 well as in their life-histories. Three peculiarities are characteris- 

 tic of most Gastropoda: (i) asymmetry, (2) a well-developed 

 head, and (3) frequently a spirally coiled shell formed of one 

 piece. 



