Figure 4: Blastula of Dreissena polymorpha Pall. (A) (from Meisenheimer, 1901) and 

 Mactra chinensis (B) (from Medvedeva and Malakhov, 1983). Legend given in the text. 



Figure 5: Gastrula (A) and trochophore (B) of Dreissena polymorpha Pall, in sagittal section 



(from Meisenheimer, 1901). 

 ate — apical tuft of cilia; bl — blastopore; fg — foregut; p — prototroch; phg — primordium of 

 hind gut; ptc — postanal tuft of cilia; rpp — renopericardiac primordium; s — shell; 



sg — shell gland. 



