322 



MARINE INVERTEBRATES 



Chiton spinosus, dorsal view. 



It will be observed from the examples given that the shell plates 

 do not entirely cover the mantle, but that a considerable portion 

 of the upper mantle surface is left exposed along the side of the 



animal. This exposed portion of the 

 mantle is called the girdle. It is always 

 very much thickened and is often ex- 

 ceedingly tough. In some species it is 

 covered by a great number of calcare- 

 ous spicules or granules which are em- 

 bedded in the leathery mantle tissue. 

 Strangely enough, the CMtonidce (a large 

 family of the Polyplacopliora) possess a 

 great number of eyes scattered over the 

 shell plates like minute dots. 



The members of this order are to be 

 found in all parts of the world, but 

 their greatest development is upon the 

 west coast of America. In California 

 the student of marine life has a splen- 

 did opportunity to examine the chitons. 

 They are generally to be found adhering 

 to the under surface of stones about low- 

 tide mark. They are very sluggish in 

 their movements and may readily be re- 

 moved from their resting-places by sud- 

 denly thrusting a knife-blade under the 

 foot and prying them off. When thus 

 detached they have a habit of rolling up 

 up into a ball and so remaining indefi- 

 nitely ; to prevent this they should be 

 placed at once in a jar of sea-water, 

 where they will resume their natural 

 position. For preservation as cabinet 

 specimens, chitons should be tied down 

 between two boards or flat substances, to hold them firmly ex- 

 tended until dried; otherwise they are apt to contract out of 

 shape. 



Six or eight species are exceedingly common upon the west 



maril 



cten 



Chiton, ventral view: an, anus; 

 cten, ctenidia ; ft, foot ; mant, man- 

 tle-edge ; mo, mouth. 



