209 



or ambulacralia. After this the paired distal oral plates develop (Figures 162, 

 163, 164). Soon after settling, rudiments of the dental plates appear between 

 the proximal oral plates. Development of the definitive skeleton of brittle 

 stars was studied by Fewkes (1887), Mortensen (1921, 1937, 1938), and 

 Hendler (1978). 



Simultaneous with the development of the juvenile organism, reduction 

 of the larval arms starts with disappearance of the anterolateral and postero- 

 dorsal arms. The posterolateral arms are retained the longest. None of the 

 fragments of the larval skeleton take part in the formation of the elements of 

 the definitive skeleton. 



Digestive system : Like other areas of the larval epithelium, the ciliated 

 band is dedifferentiated and partially resorbed. The definitive epithelium is 

 formed from the larval epithelium (Chia and Burke, 1978). 



Brittle star larvae do not feed during metamorphosis since the small 

 intestine of the larva is destroyed and resorbed; the esophagus and stomach 



Figure 162: Ophiura sarsi. 



General view of tiie larva during metamorphosis. 



al — anterolateral arms; hep — hydrocoel process; pd — posterodorsal arms; 



pi — posterolateral arms; po — postoral arms; sp — spicules, forerunners of the definitive 



skeleton. 



