PHYLUM ECHINODERMATA 



393 



3. EXAMPLE OF THE HOLOTHUROIDEA. 

 A Sea-cucumber. Cucumaria or Colochirus. 



General External Features. The body (Fig. 333) is elon- 

 gated, in shape not unlike a miniature cucumber, somewhat 

 irregularly five-sided, with an opening at each end. One end is 

 somewhat thicker than the other, and the opening at this thicker 

 (oral or anterior) end is the mouth, that at the opposite (aboral or 

 posterior) end is the anus. The body is five-sided, and along each 

 side there extends a double row 

 of podia or tube-feet. In Colo- 

 chirus there is a very distinct 

 ventral surface, into which three 

 of the five sides enter, distin- 

 guished by the absence of the 

 rows of tubercles that occur on 

 the dorsal portion of the surface, 

 and by the presence of three 

 distinct bands of tube-feet. This 

 ventral part of the body with 

 its three ambulacral areas is 

 the equivalent of the trivium 

 of the Starfish, the rest repre- 

 senting the bivium. On the 

 dorsal surface, instead of typical 

 tube-feet, there are papillae 

 devoid of sucking extremities, 

 and similar appendages take the 

 place of tube-feet at the ends 

 of the three ventral bands. In 

 Cucumaria the ventral surface 

 is less distinctly defined, but its 



position is to J)e determined by FlG . 33 3.-Cucumaria planci. Entire anima 1 

 reference to the tentacles (vide seen from the ventral surface. (From 



\ Hertwig's Lehrbuch, after Ludwig.) 



p. 394) ; there are no papillae. 



The ventral surface* is, it is to be noticed, parallel with the axis 

 joining mouth and anus, and the body, when compared with 

 that of the Starfish or Sea-urchin, is greatly drawn out in the 

 direction of the line joining mouth and anus. 



There are no definite calcareous plates ; but the integument is 

 tolerably hard, owing to the presence in its substance of innumer- 

 able microscopic calcareous spicules, very variable in shape in 

 different species of Cucumaria, and in Colochirus having the form 

 of sieve-like or lattice-like plates, some of which are to be found 

 ever; in the walls of the tube-feet. The tube-feet are, like those 

 of the Starfish, used in locomotion, progression being effected by 



