



Microns 



300 



Figure 347.— Prodissoconch of C. virginica (Gmelin). Inner view of the valves. Left valve on the left and right valve 

 on the right. Knoblike structure indicates the location of the ligament. From Ranson, 1960. 



shells still visible on tiie shells of adults. Examina- 

 tion of the many shells of adult C. virginica, C. 

 gigas, C. rhizophorae, and 0. equestris in my collec- 

 tion did not reveal the structure of their larval 

 shells, which in many instances appeared to he 

 eroded or were missing. It is doubtful tiiat 

 Ranson's method of identification of adults by 

 tlieir larval shells will gain acceptance by ta.vono- 

 mists. Comparison of liis illustrations of the 

 closely related species, such as C. virginica and 

 C. rhizophorae, indicates no significant differences 

 between the two. On the otiier hand, his set of 

 drawings of pelagic prodissoconclis may be useful 

 for planktonologists, at least for separating the 

 tlu'ee genera of ovster larvae. 



ATTACHMENT AND METAMORPHOSIS 



I-iarval life ends when the oyster attaches itself 

 to a substratum. This event is called setting, 

 settlement, or spatfall; the different expressions 

 are used interchangeably and are synonymous. 

 The word setting is commonty used bj^ American 

 biologists and oyster growers; the expressions 

 settlement and spatfall are more frequently found 

 in Canadian and British publications. The term 

 setting will be used tlu-oughout this text except in 

 quotations from other authors. 



The fully developed larva of C. virginica swims 

 with its foot projecting between the valves. 

 When the foot touches a solid sm'face, the larva 







300 



Microns 



Figure 348.— Prodissoconch of C. rhizophorae (Guilding). Arrangement as in figure 347. From Ranson, 1960. 



LARVAL DE\ELOPMEXT AND METAMORPHOSIS 365 



733-851 O — 64 24 



