■*, ,tb> 



Fig. 4. 1. Anatomy of a bivalve mollusk, Mya arenaria (after Woodward) ; left valve and 

 mantle lobe, and half the siphons, are removed: ss, respiratory siphons (the arrows indicate 

 the direction of the currents) ; aa 1 , adductor muscles; b, gills; h, heart; o, mouth, surrounded 



