10 



Figure 7: Early veliger of Cardium edule L. (from Creek, 1960). 

 m — mantle; rv — retractor of velum; sh — shell; st — stomach; v — velum. 



oral opening. Below the adoral band, under the oral opening, there is a postoral 

 ciliary band comprising one row of complex 15—20 |im long ciUa. The coor- 

 dination of the beating cilia of the pre- and postoral ciliary bands ensures, 

 according to Strathmann and his colleagues (1972), concentration of food 

 particles from the water by the ciliary band. The larger the cilia of the preoral 

 band, the greater the rate (and the lower the efficiency) of filtration of particles 

 (Strathmann and Leise, 1979). 



The rate of filtration of food particles (flagellate algae at a concentration 

 of 1.5-5.5 X 10^ cells/ml water) in M. edulis larvae is 11.4 |a.l/hr per larva 

 (Riisgard et al., 1980). At a concentration of food particles exceeding 200 |il, 

 the rate of feeding decreases (Bayne, 1976). Walne (1965) showed that larvae 

 of O. edulis efficiently capture particles from 3.0 to 8.0-9.0 ^.m in size. The 

 larvae of M. edulis cannot efficiently capture particles less than 1.0 |im or 

 more than 8.0-9.0 ^im in size (Riisgard et al., 1980). Colloidal substances in 

 suspension are not suitable for feeding; they form lumps which entangle the 

 larvae of M. edulis. At the same time, frozen or lyophilized algae and granu- 

 lated food from macrophytes and detritus are better assimilated (Mason, 1972). 

 The larvae of Crassostrea virginica and Mercenaria mercenaria do not use 

 organic debris and pure bacterial cells as food (Loosanoff, 1969). 



