XIX 



MOLPADIIDA SYNAPTIDA 



575 



extends into brackish water up the estuary. The species figured 

 (P. ephippifer) is an Antarctic one, which carries the eggs until 

 development is complete in a dorsal brood-pouch. 



..771 



-*-* Order V. Molpadiida. 



Holothuroidea with simple, finger-shaped feelers, provided 

 with ampullae ; retractor muscles 

 occasionally present; respiratory trees 

 present. Besides the feelers, the 

 only podia are five minute papillae 

 terminating the radial canals in the 

 neighbourhood of the anus. 



This order includes six genera 

 and about thirty species. Its pecu- 

 liarities seem to be due to the fact 

 that its members are burrowers, 

 leading a life like an earthworm. 

 Hence the absence of the tube- 

 feet, and the small, almost vestigial 

 character of the feelers. Trocho- 

 stoma (Fig. 262) and Caudina are 

 remarkable for the presence of a 

 tail. This appendage is in reality 

 only the narrow posterior end of 

 the body, and is especially long in 

 Caudina ; and observations on a 

 species found off the coast of 

 Maine, U.S.A., 1 have shown that Fia. 262. Troekostoma violaceum. 



,.,,.,... x 1. m, Mouth. 



the tail, like the siphon of a Mollusc, 



projects up from the burrow to the surface in order to maintain 



the respiratory current of water. 



% 



Order VI. Synaptida. 



Holothuroidea with short bipinnate (i.e. feather-shaped) feelers, 

 provided with only vestigial ampullae, and with well-developed 

 retractor muscles. Ko other podia ; radial canals absent in the 



1 Gerould, "The Anatomy and Histology of Caudina armata" Bull. Mus. Comp. 

 Zool. No. 56, 1895, p. 124. 



