Ill 



contraction pushes the food into the stomach, which is separated from the 

 esophagus by the cardinal sphincter. Food lumps are broken down in the 

 stomach where digestion takes place. The food enters the small intestine 

 through the open pyloric sphincter. Particles are sorted into edible and 

 nondigestible in the stomach. Passage of food particles through the entire 

 digestive system takes 15-20 min. According to Strathmann (1971), the 

 echinoderm larva ingests particles less than 65-85 |im in diameter and less 

 than 100-200 jim long. The rate of filtration of particles from water is 0.5 - 

 .3 |il/min. On average, filtration proceeds at a speed of 0.3-0.6 |il/min per 

 1 .0 mm of ciliated band. With an increase in concentration of algae, the rate 

 of filtration decreases. If the concentration is very high — over 5,000- 10,000 

 cells/ml — the particles cannot be handled by the ciliated band. At concen- 

 trations of algae in excess of 50,000 cells/ml, aberrations in development may 

 occur, leading to larval mortality; the intestines of such larvae are jammed 

 with food and many intact, undigested algal cells are present in the feces 

 (Strathmann, 1971; Barker, 1978). During active feeding larvae cannot be 



Figure 72; Bipinnaria of Luidia ciliaris (from Tattersall and Sheppard, 

 mp — medial projections (arms); pi — preoral lobe. 



1934). 



