238 



Figure 185: Holothuria impatiens Figure 186: Holothuria impatiens 



(Mortensen, 1938). (Mortensen, 1938). 



Arrangement of ciliated bands in the Pentactula before settling. Part of the 



doliolaria. ciliated bands of the doliolaria is retained. 



the larval integumental ephithelium transforms into the definitive. The ante- 

 rior section of the gut is modified into the larval esophagus and stomach 

 while the middle and posterior sections give rise to the small intestine. The 

 anal opening appears again (Ivanov-Kazas, 1978), as in Stichopus californicus 

 (Smiley, 1986), or the primary one is retained (Chia and Burke, 1978). 



During metamorphosis the respiratory functions are passed on from the 

 larval epithelium to the definitive ephithelium and then to the special respi- 

 ratory organs, the respiratory tree. These organs together with the so-called 

 brown bodies take upon themselves the function of excretion. As is common 

 for echinoderms, the transport of metabolites after completion of metamor- 

 phosis, is done by the hemal and perihemal systems and coelomic body 

 cavities. 



Locomotion : During metamorphosis of sea cucumbers, the locomotory 

 ftinction is performed successively by the single ciliated band of the auricularia, 

 the ringed ciliated band of the doliolaria, the primary tentacles and sometimes 

 the first ambulacral podia of the pentactula, and finally, by the ambulacral 

 podia and (or) muscles of the body wall of the definitive animal. 



In the pentactula, the ambulacral system consists of the perioral ambu- 

 lacral ring canal, from which issue the five primary tentacles and the polian 

 vesicle. Moreover, rudiments of all the radial canals are present which, start- 

 ing from the ring canal, descend along the stomach to the posterior end of the 

 larva. Ambulacral podia, except for those already present, do not form in 

 some species. 



Nervous system : The pentactula has a definitive nervous system consist- 

 ing of the nerve ring surrounding the esophagus at the base of the primary 



