27 



crm 



Figure 23: Pedal glands of the pediveliger of Ostrea edulis L. in frontal (A) and sagittal (B) 



sections (from Cranfield, 1973). 

 ar — anterior retractor; crm — cruciate muscle; dbg — duct of byssus gland; pg — pedal 

 ganglion; pr — posterior retractor; A, B, C,, C,, D-D_, — cells of nine glands of byssus 



complex. 



surfaces (Lane and Nott, 1970). The subepidermal glands participating in the 

 movement of the foot over the substrate and in the formation and attachment 

 of byssus filament occupy the maximum volume in the foot of the pediveliger. 

 Swimming pediveligers generally exhibit a negative phototaxis and a posi- 

 tive geotaxis. Their highest density is observed in near-bottom water layers. 

 While a larva is swimming, its foot may be extended, but on contacting the 

 substrate functions in larval locomotion, namely, creeping. The sequence of 

 locomotor acts during creeping are: (1) The slightly relaxed and extended foot 

 moves over the substrate by means of cilia. Glands opening on the sole exude 

 a secretion that contains weakly acidic mucopolysaccharides with a low vis- 

 cosity. Smeared on the substrate, this secretion facilitates ciliary movement. 

 (2) The anterior part of the foot is temporarily attached to the substrate 

 by means of a proteinaceous secretion, which is released by another gland 



