WORMS 185 



which the tube is closed when the worm has withdrawn itself 

 inside. The tubes are commonly found attached to shells and 

 rocks, usually solitary, but sometimes in clusters, crossing and 

 recrossing each other on the surface of the shell or rock. Plume- 

 like gills are attached to the anterior end of the body. The color 

 differs in different species. These worms may easily be mistaken 

 for the mollusks Vermetus, which live in similar tubes of larger 

 size, growing in masses. 



GENUS Serpula 



S. dianthus. Tubes often three inches long and one eighth of an 

 inch wide, the fixed end coiled and contorted, free end with circular 

 opening ; tubes often show circular ridges, marking periods of growth : 

 operculum funnel-shaped, the exterior striated and the edge bordered 

 with short processes; wreath of gills nearly circular and divided into 

 two symmetrical parts ; color variable. It is found in tide-pools, also 

 on the under side of rocks at low- water mark, either solitary or congre- 

 gated in masses, and ranges from Cape Cod to New Jersey. 



S. borealis. A minute calcareous tube, in a close, flat coil attached 

 on one side ; easily mistaken for a minute gasteropod shell ; worm has 

 an operculum and wreath of gills. Found on the fronds of seaweeds, 

 on shells, etc. 



CLASS GEPHYEEA 



This class of animals, once placed near the holothurians, be- 

 longs with the annelid worms on account of their mode of devel- 

 opment, their structure being eDtirely dissimilar. They are 

 without segments and without parapodia. The body-cavity is 

 filled with fluid and is traversed by connective tissue and fine 

 muscular fibers. They are subcylindrical animals which can 

 retract the anterior end of the body. The mouth is surrounded 

 by tentacles, or by tentacular folds, and is at the base of the 

 proboscis. They live in fissures of rocks, in sand, mud, rock, or 

 coral, and in deep gasteropod shells. Their distribution is general. 



ORDER SIPUNCULOIDEA 

 GENUS Sipunculus 



S. nud\is. The body is cylindrical, a foot or more in length when 

 extended. It is divided into two portions. The anterior end, to the 



