GONTONEMUS 



Classification : — Phylum Coelenterata, Class Plydrozoa, Or- 

 der Leptomedusae. 



Gonionemus is the medusoid or jellyfish form of a coelenter- 

 ate. In fundamental structure it closely resembles the medusa 

 of Obelia and is given as a type of medusoid instead of the 

 medusa of Obelia because of its greater size which makes it more 

 easily studied. The following study is to be made upon a speci- 

 men preserved in formalin : 



1. The convex face is called the aboral surface and the 

 concave portion the oral surface. 



2. The velum is a membrane on the oral surface which ex- 

 tends from the margin of the body inward toward the center 

 partially enclosing the bell. In many specimens that have been 

 handled roughly this membrane may be torn. Normally it is 

 perforated by a single circular opening in the center. 



3. Hanging in the center of the bell is the manuhrmm, at 

 the extremity of which is the mouth. 



4. From the stomach, at the base of the manubrium, the 

 four radial canals lead to the periphery of the disc where they 

 open into the very delicate circular canal. What is the use of 

 these canals? Study canals in specimen with aboral surface 

 uppermost. 



5. The gonads hang in folds from beneath the radial canals. 

 The eggs or spermatozoa are discharged from these directly 

 into the water. 



6. Examine the tentacles. How are the nematocysts ar- 

 ranged on them? Note the sucking disc some distance from the 

 end of each tentacle. 



7. Two kinds of sense organs can be made out on the edge 

 of the medusa. See demonstration of : 



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