PHYLUM ECHINODERMATA 



401 



3. Example of the Holothuroidea. 

 A Sea-cucumber. — Cucumaria or Colochirus. 



General External Features. — The body (Fig. 328) 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 tube-feet. In Colo- 

 chirus there is a very distinct 

 ventral surface, into which 

 three of the five sides enter, 

 distinguished 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 re- 

 presenting the bivhim. On 

 the dorsal surface, instead of 

 typical tube-feet, there are 

 papilke devoid of sucking ex- 

 tremities, and similar appen- 

 dages 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 be deter- 

 mined by reference to the 

 tentacles (vide p. 402) ; there 



are no papilla?. 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 spicides, 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 



Fio. 328 



Cucumaria planci. Entire animal 

 seen from the ventral surface. (From Hertwig's 

 Lehrbuch, after Ludwig.) 



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