118 



a 



Cc 



Figure 78: Structure of the brachiolar wall of the brachiolaria of Coscinasterias calamaria 



(from Barker, 1978). 

 ax — axons of nerve cells; bl — basement membrane; cc — coelomic lobe; ce — coelomic 

 epithelium; cf — collagen fiber; cl — cilia; ct — connective tissue; eye — cytoplasmic 

 processes of muscle cells; db — dense body; m — mitochondria; mv — microvilli; va — 



vacuolated cells. 



Locomotion : This is performed by means of cilia in the ciliated band. As 

 the body and processes grow, the size of the band increases and the processes 

 usually become long flexible arms. The elongate ciliated band enables the 

 brachiolaria to continue swimming as the definitive star develops. The move- 

 ment of the brachiolaria becomes more rapid and more complex. The larva 

 may reverse directions not only by describing a loop through flexion of the 

 dorsal side of the body, but also by changing the position of its arms. On 

 coming into contact with an obstacle, the brachiolaria extends its posterolat- 

 eral, posterodorsol, and postoral arms forward, while directing the mediodorsal 

 process ventrally. The water current generated in this action by the ciliated 

 band, which is directed forward, moves the larva in the opposite direction. 

 Flexion of the processes and arms of the brachiolaria occurs through contrac- 

 tion of the muscle fibers connecting the processes with the larval body (Fig- 

 ure 79) (Strathmann, 1971). 



Nervous system and sense organs : In addition to the above-described 

 nervous system of the bipinnaria, a neuropyle-axon plexus develops in the 

 brachiolaria, which is situated apically, at the base of the brachioles and 



