PHYLUM ANNELIDA 



Class : Chcetopoda. Order : Polychceta 

 THE SANDWORM (NEREIS) 



Nereis is a common marine worm which Hves in the sand along 

 the shores of our northern and middle states. Its food consists of 

 various kinds of small marine animals, which it catches with its 

 formidable, protrusile proboscis. A specimen should be selected 

 for study in which the proboscis is not thrust out. 



Observe, in the first place, the long, segmented, and some- 

 what flattened body, the pair of appendages on each segment, 

 and the distinct head with special sense organs at the forward 

 end ; observe also that the body tapers toward the hinder end, 

 where is a pair of special sense organs, the long caudal feelers. 

 All these characters indicate an animal possessed of the power 

 of rapid locomotion. Count the somites, or body segments ; note 

 that they are almost exactly alike. This lack of specialization is 

 in sharp contrast to the condition of the somites in most arthro- 

 pods. Observe carefully the appendages ; they differ from those 

 of the arthropod in that each one is an unjointed expansion of 

 the body wall, whereas the arthropod appendage is segmented. 

 Each one is made up of several lobes and is provided with long 

 bristles, or setae. Note the absence of a hard shell, the external 

 integumentary covering being the glistening cuticula, which has 

 not been stiffened by the presence of calcareous salts. 



Observe the head and the forward portion of the body. An 

 annelid's body is composed genetically of two portions: the 

 prosoma, or primitive head, and the metasoma, or the primitive, 

 segmented trunk. The prosoma may be further divided into the 

 prostomium, which lies in front of the mouth and contains the 

 brain and the principal organs of special sense, and the metasto- 

 mium, which contains the mouth. In Nereis the prostomium 



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