26 



Figu.e 22: F(k>1 (ii the pediveliger of Ostrea ediilis L. ventral view (from Cranfield, 1973). 



According to Creek (1960), in the pediveliger of Cardium edule the larval 

 retractor of the foot is fiinctional, and is replaced by a definitive structure once 

 the larva has settled on the bottom. The posterior pair of retractors is attached 

 to the shell in the region of the posterior adductor; these muscles then pass 

 between the visceral ganglion and one of the pedal glands and are inserted in 

 the ventral surface of the foot. The anterior pair of retractors originates on the 

 dorsal side of each valve before the hinge line. These retractors pass along the 

 sides of the digestive tract and bending around the pedal ganglion, are inserted 

 in the dorsal surface of the foot along both sides of the ftirrow. The longi- 

 tudinal muscles of the dorsal and lateral sides of the foot are attached along 

 the dorsal side of each valve near the anterior adductor of the shell. The 

 cruciate muscles participate in turning the foot, connecting its left and right 

 sides to the opposite valve (Figure 23) (Cranfield, 1973). 



The foot is covered with a ciliated epithelium. Each ciliated cell bears 

 numerous microvilli. The cilia are irregularly arranged on the surface of the 

 foot and are dense and very long at its tip and on its ventral and ventrolateral 



