124 PHYLUM ECHINODERMATA 



Class : Holothurioidea 

 A SEA CUCUMBER 



Two common species of holothurians which Uve in the shallow 

 water of the New England coast are suitable for this dissection : 

 Thyone briareus and Cucumaria frondosa, the former being com- 

 mon in Vineyard and Long Island Sounds, and the latter on the 

 Maine coast. The latter is the larger of the two species, being from 

 ten to twenty-five centimeters or more long and about half as 

 thick, and differs from Thyone, among other things, in having 

 ambulacral feet in the radial areas alone ; thus it possesses five 

 broad bands of these appendages, the interradial areas being 

 smooth. Thyone is from eight to about twenty centimeters long 

 and five centimeters thick, and is covered with ambulacral feet, 

 the five broad radial bands meeting in the interradial areas. It 

 will be used as the basis of this dissection. 



Observe the form and color of the body. Note that the upper 

 and lower sides are distinctly differentiated, the former having 

 fewer feet than the latter. In the center of the forward end is 

 the mouth, surrounded by ten branched tentacles, by means of 

 which the animal collects the minute organisms which constitute 

 its food. Above the mouth and between the bases of two ten- 

 tacles is the genital pore. In the center of the hinder end is the 

 anus, surrounded by five anal teeth. The main longitudinal axis 

 of the body (that which joins the mouth and the anus) will thus 

 be seen to be very long, in sharp contrast to that of the starfish 

 and sea urchin, in which it is much shorter. In consequence of 

 this feature the body is elongate and more or less wormlike, and 

 the animal does not rest on the oral^ surface but on its side. 



Exercise 1. Draw a side view of the animal and label carefully all 

 the features observed. 



With strong scissors cut the body open by a longitudinal slit 

 along the underside. Place it in a pan of water and with large 

 pins fasten down the two sides of the body wall on the right and 

 left. Without cutting any of them, study the internal organs. 



