Figure 8: Veliger of Ostrea edulis L. (from Erdmann, 1935). 



a — anus; aa — anterior adductor; ap — apical plate; bg — byssus gland; bl — buccal lobe 



(plate); csg — gland of crystalline style; dg — digestive gland; es — esophagus; m — mouth; 



mc — mesenchymal cells; pn — protonephridium; rv — retractor of velum; st — stomach; 



V — velum; wmc — wall of mantle cavity. 



A positive relationship has been established between rate of larval groM^h 

 and number of cells caught by the larva. Flagellate algae, such as Monochrysis 

 and Isochrysis, devoid of a cell wall and forming no toxic substances, consti- 

 tute a better food for larvae (Ukeles, 1969, 1975). At a low concentration of 

 food particles, the rate of filtration and its efficiency increase. 



The postoral tuft of cilia lies in the buccal region and is formed by the 

 postoral ciliary band. According to Waller (1981), these cilia may have a 

 sensory function or facilitate expulsion of excess mucus and excess food from 

 the mouth. 



The oral opening, situated at the edge of the lower part of the velum, leads 

 to the esophagus. Cells of the esophagus contain vacuoles and bear powerful 

 cilia that fill the lumen of the esophagus and project exteriorly through the oral 

 opening. The next section of the digestive tract is the stomach. The gastric 

 cells contain vacuoles; cilia are absent. The digestive gland or liver consists 



