VERMES 115 



Malacobdella grossa Miiller 



A small flat worm of leech-like form that lives 

 as a commensal in the Clam (Venus mercenaria) and 

 other bivalves. 



NEMATHELMINTHES 



(Round Worms, Thread Worms) 



Round, unsegmented worms, a large number of 

 which are parasitic, However, great quantities of 

 minute thread worms are to be found in sea water. 

 If one examines a few drops of sea water under a 

 microscope, particularly water containing some 

 algae or sea weeds, one can see these tiny thread 

 worms constantly coiling and uncoiling themselves. 

 Many species have been described, but since they 

 are all very minute and difficult to determine, they 

 are not discussed here. 



CHAETOGNATHA 



(Glass Worms) 



Elongate, unsegmented worms with two or three 

 pairs of fins. 



Sagitta elegans Verrill (Arrow Worm; Glass Worm) 



Slender, transparent and very minute (about 3 

 mm. long) ; three pairs of fins. Various species of 

 Sagitta, often of larger size, are abundant in all seas. 

 S. elegans is known from Chesapeake Bay northward. 



