119 



Figure 79: Flexion of processes of tiie brachiolaria of Pisaster ochraceus during reversal of 



movement (from Strathmann, 1971). 



A — locomotion; B — reverse movement. 



under the epithelium of the adhesive papillae and the disk (Barker, 1978b; 

 Burke, 1983). Here one also finds an accumulation of serotonergic neurons 

 (Bisgrove and Burke, 1987). The nerve cells of papillae and brachioles are 

 connected with processes from the preoral nerve strands (Nazlin and Dautov, 

 1987). Among the cells of the papillae and disk. Barker identifies neurose- 

 cretory cells that presumably participate in the attachment and adhesion of the 

 brachiolaria to the substrate. The only specialized sensory cells (if we do not 

 consider the presumed sensory cells described in the section on the bipinnaria) 

 are the ciliated cells of the adhesive papillae of the brachiolar arms. The basal 

 part of such cells reaches the subepithelial axon plexus. The lone cilium 

 surrounded by microvilli has a developed kinetochore. Probably the brachiolaria 

 uses these cells to probe the substrate for a suitable place to settle. 



Attachment system : The attachment system of a brachiolaria typically 

 comprises three brachiolar arms, an attachment disk, and lateral papillae 

 (Figure 80). Lateral brachiolar arms appear only in the brachiolaria stage; the 

 medial arm is a modified medioventral process. During transformation into a 



