116 



Figure 77: Bipinnaria of Astropecten auranciacus (from Horstadius, 1939). 



abd — aboral disk of definitive sea star; ac — axocoel; es — esophagus; g — gut; Ihc — left 



hydrocoel; pocb — postoral ciliated band; prcb — preoral ciliated band; st — stomach. 



in the esophagus, and two types of nerve cells situated in the ciliated band: 

 one linked to the axonal tracts and the other provided with cilia. On the lower 

 lip, in the comers of the larval mouth, clusters of nerve cells occur. In the 

 bipinnaria of Asterias amurensis the presence of numerous seratonergic nerve 

 cells has been demonstrated along the ciliated band (Nakajima, 1987). 

 Bipinnariae do not have developed sense organs; however, it is quite possible 

 that ciliated nerve cells of the ciliated bands perform sensory functions (Burke, 

 1983). 



Integument : Echinoderm larvae lack a specialized protective organ, equiva- 

 lent to the larval shell of bivalves — an organ that performs several functions 

 simultaneously. Hence protection of the internal tissue of the larva against 

 adverse effects is solely delegated to the cells of the integumentary epithe- 

 lium, which bear cilia and microvilli and produce mucus. 



Rudiments of definitive organs : The development of sea stars from 

 planktotrophic larvae may proceed in two ways. In most sea stars there is a 

 brachiolaria stage immediately following the bipinnaria stage, during which 

 development of the organs of attachment and anchoring of the definitive body 

 of the organism are characteristic. Metamorphosis concludes with the attach- 

 ment of the larva to the substrate. In sea stars of the families Luidiidae and 

 Astropectinidae, organs of attachment do not appear during development; 



