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selective, accepting some and rejecting other species of algae; however, the 

 rate of filtration differs for different species of algae. Moreover, one species 

 of algae may influence the rate of filtration of another species — increasing 

 or decreasing it (Strathmann, 1975). The nutritional value of different food 

 particles has not been thoroughly investigated. Adequate data are not available 

 for judging the role of bacteria and soluble organic substances in the nutrition 

 of larvae of sea stars. But their role can hardly be important since the ciliated 

 band poorly retains particles less than 2—3 jim in size and observations have 

 shown that growth mainly occurs with active feeding on phytoplankton. 



Like sea urchins (Chia and Burke, 1978), it has been suggested that 

 reserve food, primarily in the form of lipids, is stored by the larvae of sea 

 stars in cells of the digestive tract. 



Respiration : As in larvae of bivalves, the intake of oxygen and removal 

 of carbon dioxide in the larvae of sea stars occurs by diffusion. The minute 

 size of the larvae enables them to dispense with any specialized system. Their 

 constant motion — beating of ciliated bands, movement of other areas of the 

 body surface, and activity of the ciliated surface of the digestive system — 

 is conducive to gaseous exchange. 



Transport of substances: In echinoderm larvae (as in larvae of other 

 marine invertebrates), which are minute in size, there is no need for a special 

 system for blood circulation. This function is fulfilled by extensive — pri- 

 mary and secondary — body cavities. Transport of substances in the primary 

 body cavity is facilitated by contraction of the body wall and esophagus, and 

 transportation of substances in the secondary cavity (coelom) facilitated by 

 beating of cilia lining the coelomic cavity. 



Excretion : Larvae of sea stars possess no specialized excretory system. 

 The function of excretion, as in many lower groups of animals, is performed 

 by the developed digestive system. Evidently, mesenchymal cells participate 

 in the removal of metabolic products; these cells are scattered in the primary 

 body cavity. Possibly Field (1892) is correct, as his demonstration of the 

 excretory function of the pore canal is partly confirmed by the organized 

 directional movement of cilia in the coelomic cavities (Gemmill, 1914), 

 which causes a current in the direction of the pore canal. Ruppert and Balser 

 (1986) are more specific in naming the canal-hydropore complex the 

 nephridium. 



In the course of development of sea stars the coelomic structures undergo 

 considerable transformation. They form various organs and systems in the 

 definitive organism, primarily its ambulacral system. We do not' propose to 

 describe the development and transformation of coeloms; rather, we shall 

 describe only the coelomic formations of bipinnaria, since these are multi- 



