23 



Figure 19: Ridges and furrows on lateral surfaces of teeth and alveoli of veliger valve of 

 Mizuhopecten yessoensis. 



veliger since they fiinction only in the later larva — the pediveliger. The first 

 group comprises rudiments of gills, renopericardic complex, some elements of 

 the nervous system, rudiments of the foot, byssus gland, some sense organs, 

 and the reproductive system. In view of the secondary simplification of the 

 adult organism, in some mollusks the foot, byssus gland, and sense organs — 

 eyes and statocysts — exist only in the later periods of larval life. Such, in 

 particular, is the case in ostroids and pectinids. 



The stages of the developed veliger with umbo and the last larval stage — 

 the pediveliger — are often combined in the term veliconcha or veliconch, 

 which was introduced by Werner (1939). 



Pediveliger 



In this stage the larva, having attained maximum size, bears a functional 

 foot with which it can creep, while simultaneously retaining the ability to swim 

 by means of its developed velum (Figures 20 and 21). The ultimate objective 

 of the pediveliger is to select and colonize a substrate and then to change over 

 to a definitive mode of feeding and locomotion. Hence the pediveliger char- 

 acteristically has functional sense organs — eyes and statocysts, and a func- 

 tional organ of locomotion and attachment, the foot. Concomitant with these 

 larval organs, definitive organs are present in the body of the pediveliger. 



