FEATHER STARS. 243 



have ampullae and tube feet, as in sea urchins. But there 

 are many divergences, especially in the reduction of the tube 

 feet areas. Instead of tube feet, or along with them, there 

 are often conical processes or papillae without terminal discs. 

 These are especially common on the dorsal surface. The 

 blood vascular system is not very definite, and seems to con- 

 sist mainly of spaces in the connective tissue, e.g., around the 

 pharynx and along the intestine. 



The sexes are usually separate. The reproductive organs 

 do not exhibit radial symmetry, and are branched tubes 

 which open within or just outside the circle of tentacles. 

 They and other internal organs of Holothurians are often 

 very brightly coloured. The larva is, in most cases, what we 

 shall afterwards describe as an Auricularia. Sometimes, 

 however, the larval stage is skipped, as in Cucumaria crocea 

 and Psolus ephippiger where the eggs and young are attached 

 to the back of the mother. In Cucumaria lavigata there 

 is an invaginated brood pouch; in Synapta vivipara and 

 others the body cavity serves as a brood pouch. 



The calcareous plates of Holothurians are found as far 

 back as Carboniferous strata. 



Classification. 



1. Elasipoda : primitive deep sea forms, bilaterally symmetrical, with 



tube feet on the ventral surface only, and with papillae on 

 the back. The stone canal often opens externally by a 

 pore. There are no respiratory trees. 

 e.g.) Kolga, Elpidia. 



2. Pedata : with well-developed tube feet and papillae. 



e.g., Holothuria, Cucumaria, Psolus. 



3. Apoda : without radial canals, tube feet, or respiratory trees. 



e.g., Synapta, a remarkable animal, especially apt to break 

 in pieces ; pinnate tentacles ; hermaphrodite ; with 

 beautiful calcareous anchors and plates in the skin. 

 Semper has described a strange animal, Rhopalodina lageniformis , 

 from the Congo coast. It is like a globular flask, with mouth and anus 

 close together at the narrow end, with ten ambulacral areas. 



Class CRINOIDEA. FEATHER STARS. 

 Commonest Type, Antedon rosaceus. 



The feather stars or sea lilies differ from other Echino- 

 derms in being fixed permanently or temporarily by a jointed 



