123 



Respiration : The respiratory function is transferred from the larval to 

 the definitive epithelium. In the juvenile sea star visceral coeloms formed 

 from the larval somatocoels and the hemal and perihemal systems formed 

 from the left somatocoel and axocoel, also participate in the transportation 

 of substances. 



Elimination of metabolic products : This involves several structures — 

 spheroid bodies with phagocytes, the axial organ, and the rectal glands 

 (Bachmann and Glodschmid, 1978; Jangoux, 1978; Hobaus, 1979). Larval 

 coeloms are considerably transformed; with their participation, a new loco- 

 motor organ, hemal and perihemal systems, axial organ, and coelomic cavity 

 of the definitive sea star are formed. 



Locomotion : With a changeover to a benthic mode of life, the sea star 

 loses its swimming organ — the ciliated band. The transient locomotor appa- 

 ratus of the brachiolaria — the brachioles — remains for a very short time, 

 allowing the sea star to move on the substrate. At this stage there occurs, so 

 to speak, a testing of a new locomotor mechanism through the assistance of 

 the apically papillate body processes, into which coelomic processes pen- 

 etrate. The definitive locomotor organ — the ambulacral system, which arises 

 during metamorphosis — works on a similar principle. The region of the left 

 hydrocoel plays a leading role in its formation; bending, the two ends later 

 merge and form the rudiment of the oral ring of the ambulacral system. From 

 the arc issue hydrocoelic processes — rudiments of the radial canals of the 

 ambulacral system (Figure 83). The terminal areas of these canals, in conjuntion 

 with the ectoderm surrounding them, later give rise to the terminal tentacle 

 (podia), while along the sides of the canal secondary processes form — ^rudi- 

 ments of the ambulacral podia. The axocoel takes part in the formation of the 

 stone canal fi^om the larval pore canal and the hydropore (Gemmill, 1914). 



Nervous system and sense organs : The larval nervous system and sense 

 organs are replaced by definitive ones. In the opinion of Gemmill (1912), the 

 nerve plexus of the preoral lobe of the brachiolaria participates in the forma- 

 tion of the oral ring of the definitive nervous system. The most developed 

 ectoneural system in sea stars is formed from the thickened ectoderm above 

 the circumoral ring and radial canals of the ambulacral system. In addition 

 to sense organs scattered in the integument, numerous sensory elements are 

 located in the terminal tentacle and ocelli at the base of the tentacle. 



Integument : A variety of skin glands, spines, pedicellaria, and other ele- 

 ments of the skeleton of the definitive sea star perform protective ftinctions. 



Skeleton : The definitive skeleton has already begun to form in the 

 bipinnaria. In sea stars, as in all echinoderms, the skeleton is internal and of 



