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The bootlace worm, Lineus lon^issimus, a fragile nemertean that is often many yards long. At 

 low tide it hides under rocks or in the holdfasts of kelps. (England. M. A. Wilson) 



sheathed in a muscular tube that lies above the diges- 

 tive tract. 



As it goes on mostly at night, feeding is not often 

 observed. The favored food seems to be annelids, 

 and these have been seen to be swallowed whole, 

 making a prominent bulge in the thin, elastic body 

 of the nemertean. Mollusks, crustaceans, and fishes 

 are also eaten, though bigger prey may be sucked at, 

 not downed in one piece. Undigested residues do not 

 have to be cast out the mouth, for the nemerteans are 

 the lowest animals that have an anus, a second open- 

 ing to the digestive tract, which voids materials from 

 the rear end of the animal. The ribbon worms are 

 built much like flatworms, but aside from the anus 

 they can boast another important improvement. They 



have contractile blood vessels. Waves of contraction 

 in the strong muscles of the body wall also help to 

 push blood and food along their respective tubes, 

 and in a worm at rest it is these powerful muscular 

 waves that are seen to pass along the body. 



A few ribbon worms swim by undulations of the 

 long body. The young and the smaller forms glide 

 along, by means of beating cilia on the body surface, 

 over a lubricating bed of secreted slime. In larger 

 worms more use is made of muscular contractions for 

 creeping. Some even spiral ahead at times by agile 

 body contortions. 



One may grasp several inches of a delicate, slimy 

 nemertean and pull cautiously lest it break, yet have 

 it slip from one's fingers and disappear down a crack 



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