133 



Figure 88: Bipinnaria of Patiria 

 pectinifera. 



typical coeloblastula forms with a unilayered 

 blastoderm and an extensive blastocoel; rotating 

 by means of cilia in its envelope, the coeloblastula 

 then exists from it (see Figure 66). Gastrulation 

 begins 16-20 hr after fertilization; it occurs by 

 invagination accompanied by slight unipolar im- 

 migration of the mesenchymal cells. The gas- 

 trula is 250 |im x 200 |im in size. Coeloms grow 

 faster than in larvae of the family Asteriidae. 

 After a relatively short dipleurula stage, the larva 

 becomes a bipinnaria. 



Bipinnaria 



The bipinnaria of Patiria is characterized by 

 relatively undeveloped and less movable pro- 

 cesses (Figure 68). Pigment is absent in the di- 

 stal ends of the processes. The left and right 

 axocoel grow forward and merge and the single 

 axo-hydrocoel encompasses the oral cavity with 



Figure 89: Patiria pectinifera. 

 Formation of definitive siceleton. 



