PHYLUM ECHINODERMATA 



369 



ilcareous rods. A metamorphosis, in which the bilateral larva 

 becomes converted into the radial adult, takes place as in 

 Starfish. 



3. EXAMPLE OF THE HOLOTHUROIDEA. 

 A Sea-Cucumber. Cucumaria or Colochirus. 



General External Features. The body (Fig. 299) 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 open- 

 ing 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 

 Colochirus there is a very 

 distinct ventral surface, into 

 which three of the five sides 

 enter, distinguished by the 

 absence of the rows of tuber- 

 cles that occur on the dorsal 

 portion of the surface, and 

 by the presence of three dis- 

 tinct bands of tube-feet. 

 This ventral part of the body 

 with its three ambulacra! 

 areas is the equivalent of the 

 trivium of the starfish, the 

 rest representing the bivium. 

 On the dorsal surface instead 

 of typical tube-feet there are 

 papillse 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 always to be 

 determined by reference td the tentacles (vide infra) ; there are no 

 papiHse. The ventral surface is, it is to be noticed, parallel with 

 the axis joining mouth and anus, not at right angles with it as in 

 e Starfish and Sea-urchin, and the body is, when compared with 

 eirs, greatly drawn out in the direction of the line joining mouth 

 d anus. 



FIG. 299. Cucumaria planci. Entire animal 

 seen from the ventral surface. (From Hurtwig s 

 Lthrbuch, after Ludwig.) 



VOL. I 



B B 



