227 



Figure 173. Caudina chilensis (Inaba, 1930). 



Early stages of division. 



A — 4 blastomeres; B — 8 blastomeres; C — 16 blastomeres; pb — polar bodies. 



In Caudina chilensis, as in some sea stars, several invaginations enter the 

 blastula cavity, depressions marking them on the surface (Inaba, 1930) 

 (Figure 175). Folos remain up to the beginning of gastrulation when they 

 begin to gradually smoothen. A wrinkled blastula has also been reported in 

 Cucumaria normani and C. saxicora (Kume and Dan, 1968). 



Figure 174. Cucumaria frondosa 



(-Psolinus brevis). 



(Kowalewsky, 1867). 



Blastula. Blastocoel is well developed. 



Figure 175. Caudina chilensis (Inaba, 



1930). 



Wrinkled blastula. General view. 



In species in which development occurs in the body of the adult indi- 

 vidual, the blastula remains immobile. Such a blastula is found in Holothuria 

 floridana (Edwards, 1909), Synapta vivipara (Clark, 1898, 1910), Chiridota 

 rotifera (Clark, 1910), and Thyone briareus (Ohshima, 1925). 



Gastrula 



In Ophiodesoma grisea and Holothuria difficilis the gastrula is formed 

 10 hrs after fertilization (Mortensen, 1938). Development of the gastrula 

 takes 1 8 -20 hrs in Synaptula reciprocans, Holothuria impatien, H pardalis. 



