THYONE BRIAREUS Lesueur 



Material. Thyone briareus is found along the Atlantic 

 Coast below low water mark on muddy bottom. Like all holo- 

 thurians they are liable to throw out their viscera when put in 

 a preserving liquid. Various methods have been recommended 

 to overcome this difficulty. Perhaps the simplest is that of 

 seizing the animal below the tentacles with a strong forceps and 

 plunging it into boiling water. After that they may be pre- 

 served in alcohol or formalin. For the study of the ambulacral 

 system the specimens should be injected through a Polian 

 vesicle. 



Descriptive Part 



Thyone briareus is a common representative of the Class 

 Holothurioidea. Although following the plan of radial sym- 

 metry it little resembles the other Echinodermata. Its body is 

 elongated and considerably narrowed towards the anterior end 

 which is provided with branched tentacles surrounding the 

 month. Moreover, the animal does not crawl on its oral surface, 

 but uses for this purpose the three radii thickly covered with 

 ambulacral feet. This surface is therefore physiologically the 

 ventral one, while the dorsal one is represented by the remaining 

 two radii. The bilateral symmetry is besides greatly accen- 

 tuated by the position of the anus at the end of the body and 

 the presence of a single genital opening between the tentacles 

 on the interradius opposite the median radius of the ventral 

 surface. The ten oral tentacles correspond to the ten oral 

 papillae of the sea-urchin and represent the first five pairs of 

 modified ambulacral tubes. The median ventral pair of tentacles 

 is considerably smaller than the others. It is customary to 



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