SEA WORMS. 



285 



dance on the backs of old oyster shells, &c.) secrete 

 a calcareous tube, as compact as the valve of a 

 mollusc. The crimson plumes are protruded from 

 the upper part, and these sweep the water for fresh 



Fig. 216. 



Tube of Terebella. 



Sabella unispira. 



air. In colour they are very contrasted with the 

 larger and still more feather-like gills of the Sabella 

 a large marine worm, to be seen in marine tanks 

 burrowing in sand, or affixed to stones which are 

 generally of a dull grey, although they are sometimes 



