12 



Figure 9: Velum of the veliger of Ostrea edulis L. (from Waller, 1981). 



of two pouches (lobes) arising from the stomach (see Figure 8). The cells of 

 the liver vacuolize later. The right lobe of the liver is larger than the left and 

 shifted backward. Cells of the digestive gland are marked by larger size and 

 sometimes by color — greenish or reddish-brown depending on food. Accumu- 

 lated granules of food matter are visible in them. Neutral lipids, and not 

 glycogen as in adult mollusks, are the principal energy reserve of larvae 

 (Holland and Spencer, 1973; Holland, 1978). A changeover to the new reserve 

 nutrients takes place in three- to five-month-old spat (Holland and Hannant, 

 1974). The large liver allows us to suggest a storage ftinction for this organ; 

 a large part of the reserve nutrients is consumed during metamorphosis and in 

 the initial period after settling on the bottom, during which the larva does not 

 feed (Holland and Spencer, 1973). It may be that together with such large 

 cells, the larval liver contains small undifferentiated cells of the ftiture defini- 

 tive liver. 



The gland of the crystalline style forms on the right side of the posterior 

 part of the stomach. It is lined with cilia. At the end of larval life, or after the 

 larva settles to the bottom, the cells of this gland secrete the crystalline style 

 containing digestive enzymes. Behind the stomach lies the small intestine, 

 which forms a loop, and in the larvae of M edulis the blind gut (Bayne,1971). 

 In the early veliger the gut may lack a lumen and resemble a cylinder of 

 closely packed cells (La Barbera, 1975). The gut epithelium is simple, flat- 

 tened, and bears cilia. The small intestine passes into the short hind gut — ^the 

 proctodeum — ^with vacuolated cells. The proctodeum opens exteriorly through 

 the anus; cilia are visible in its lumen. 



