2i6 ECHINODERMATA. 



X. Apoda : without tube-feet or papillse. , 



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

 in pieces, without even radial water- vessels, without 

 respiratory trees or Cuvierian organs; herma- 

 phrodite; 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 very globular flask, with mouth and 

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



Class Crinoidea. Feather-Stars. 



Commonest Type, Antedon rosacea. The Rosy 

 Feather-star. 



The feather-stars or sea-lilies differ from other Echino- 

 derms in being fixed permanently or temporarily by a jointed 

 stalk. The modern Comatulids, e.g., the rosy feather-star 

 ( Comatula or Antedon rosacea) leave their stalk at a certain 

 stage in life; but the others, e.g., Pentacrinus, are permanently 

 stalked like almost all the extinct stone lilies or encrinites 

 once so abundant. Most of them live in deep water, and 

 many in the great abysses. An anchorage is found on rocks 

 and stones, or in the soft mud, and great numbers grow 

 together — a bed of sea-lilies. The free Comatulids swim 

 about by bending and straightening their arms, and they 

 have grappling " cirri " on the aboral side, where the relin- 

 quished stalk was attached. By these cirri they moor them- 

 selves temporarily. Small organisms — Diatoms, Protozoa, 

 minute Crustaceans — are wafted down ciliated grooves on 

 the arms to, the central mouth, which is of course on the 

 upturned surface. Some members of the class, e.,^., C(?waft</a, 

 are infested by minute parasitic " worms " (Myzostoma) allied 

 to Chsetopods, which form galls on the arms. A lost 

 arm can be replaced, and even the visceral mass may be 

 renewed. 



The animal consists of (i) a cup or calyx, (2) an oral disc 

 forming the lid of this cup, (3) the radiating " arms," and (4) 

 the stalk supporting the whole. 



The calyx consists of apical plates (corresponding to the 

 apical plates of the sea-urchin), to which radials belonging 

 to the arms and other accessory plates are often added. In 

 a few extinct genera with no stalk the dorso-central plate has 



