202 



Figure 154: Ophiothrix fragilis (McBride, 1907). 



General view of pluteus I stage. 



al — anterolateral arms; pi — posterolateral arms; po — postoral arms; talb — transverse 



anterolateral band; tpob — transverse postoral band. 



secretion produced by them helps to trap and to move food particles along the 

 band. The food which reaches the oral opening is transported to the esophagus 

 by means of the cilia in the oral cavity. All sections of the gut are provided 

 with cilia. When the food enters the esophagus, it is transported up to the 

 cardiac sphincter. As the latter opens, which is accompanied by a contraction 

 of the esophageal muscles, the food clump passes into the stomach. Here the 

 food is sorted. Strathmann (1971) demonstrated that when ophioplutei were 

 fed a mixture of algae and carmine particles, the latter were soon discarded 

 by the larvae, while the algae remained in the stomach for a long time. The 

 rate of passage of food particles through the gut may be regulated by the 

 speed with which the particles circulate in the upper part of the stomach and 

 gather near the pyloric sphincter, from where they enter the small intestine 

 and, upon contraction of the gastric muscles, are egested. 



Brittle star larvae filter from the plankton microalgae that do not exceed 

 65 \\,m in diameter and 150 jim in length. These algae comprise various 

 species of Amphidinium, Cricosphaera, Phaeodactylum, Dunaliella and 

 others. The rate of filtration of food particles from the plankton varies from 

 1.8 to 3.0 ml/min. 



In addition to sorting food in the stomach, brittle star larvae, like other 

 echinoderms, can eject too large algae from the oral cavity or esophagus. For 

 expulsion of such objects from the esophagus, the oral opening is enlarged, 

 the direction of beating of the adoral band cilia changes, and the esophageal 

 muscles contract. Enlargement of the oral opening by raising the preoral band 



