52 



A7/ierica?i Seashells 



Identification of Chitons 



It is essential for accurate identifications to refer to one or more ot the 

 ten technical terms used in describing the various parts of the chiton. A few 

 minutes' study of figure i8 will prepare the reader for the photographs, 

 identification drawings and descriptions of the species. Jumping to conclu- 

 sions from the photographs instead of ascertaining the family or genus first 

 will lead to discourag-ino- results. 



EXTERIOR 



INTERIOR 



ORRNuLes 



f^NTeRioR vAt-ve 



Rl^OlftLLY RtftftEO 



nEDiftN vftLvea 



LftTERRU M«E« 



RftOlADiALuY NOOi^LOse 



DlVftRlCAT|N& LINES 

 TU&UM 



Pleural tract 

 central area 



MUCRo 

 POSTtRiOA V(\LVE 



INSERTION 



pLAie TEETH 



5VJTU8R1. Pl_flr£ 



Figure i8. Parts of the chiton shell. 



All the chitons discussed in this book bear eight shelly valves which 

 cover the body of the creature and are bound together by a leathery girdle. 

 The chitons without valves (Aplacophora) are too rare to be conveniently 

 included here. A view of the underside of a living chiton will show the 

 rather small, separate head and its mouth and, behind this, the larger, ob- 

 long foot. On each side of the foot is a straight row of closely packed gills. 

 The head bears no tentacles or eyes, although the valves of many chitons 

 bear numerous shell eyes. 



Each chiton possesses three types of valves: (i) the anterior valve at 

 the head end, (2) six intermediate valves, and (3) the posterior valve at 

 the hind end. The shape and ornamentation of these valves are used for 

 identification purposes, and for this reason the various areas of the valves 

 have been named. Removal of the last two valves by the soaking of dried 



