•Anterior adductor 

 Anterior retractor 

 Protractor 



- Posterior retractor 

 Posterior adductor 



Posterior 

 Incurrent siphon- 

 Excurrent siphon 



Lines of 

 growth 



Anterior 



Mantle line 

 A 



B 



Figure 172. Freshwater clam. A, inside view of a valve showing point of attachment of 

 mantle and points of attachment of muscles. B, external view of a livnig animal with foot 

 protruding from the shell and arrows showing direction of water flow through the siphons. 



Periostracum Prismatic layer Nacreous layer 



(mother of pearl) 



OJI 



Mantle < 



Ciliated outer 

 c epithelium 



Foreign body (sand or 

 a parasite) between 

 shell and mantle 



Pearl formed by 

 secretion of nacre 

 around foreign body 



Figure 173. Enlarged cross section of the shell and mantle of a fresh-water clam. Note the 

 pearl being formed between the shell and mantle by the nacre-secreting cells. 



284 



