CHAPTER XVII 



Feather-duster worms in tubes and a paddle-footed 

 worm creeping on bottom 



The Segmented Worms 



{P/iyln/N Ainielida) 



o 



F all the many kinds of worms, those with seg- 

 mented bodies are surely known to more people than 

 any others. Thus the inland angler seeks an earth- 

 worm as a lure, and the coastal fisherman realizes 

 that in salt water a sea worm will remain attractive 

 longer to fish, and therefore baits his hook with a 

 ragworm. 



Just about everyone sooner or later wades bare- 

 foot in a pond or stream where bloodsucking leeches 

 live, and finds these parasites attracted to his own 

 skin. In many parts of the world, pharmacies main- 

 tain a supply of live medicinal leeches, whether to 

 take the color from a black eye or to extract "bad 

 blood" from a patient. 



The earthworm, the ragworm, and the leech are all 

 segmented worms. The same phylum includes the 

 far smaller Enchytraeiis and Tiibifex, worms sold in 

 pet stores as food for aquarium denizens. 



The rings that mark the body of an earthworm or 

 ragworm are the features giving the phylum Annelida 

 its name, from a French corruption of the Latin 

 anellis, a ring. Each of the encircling grooves corre- 

 sponds to the boundaries of an internal partition di- 

 viding the body into a series of almost identical seg- 

 ments. Many of these segments have not only a priv- 

 ate portion of the worm's body cavity, but also a local 

 exchange station (ganglion) of its nervous system, a 

 pair of excretory tubules (nephridia), and access to 

 the products of digestion both directly from the walls 



of the digestive tract and from blood vessels which 

 extend through all segments from one end of the 

 worm to the other. 



The anterior segments of an annelid worm show 

 specializations related to feeding. It is here that the 

 worm has a particularly important part of its nervous 

 system, even when no head is recognizable. Most 

 annelids can survive loss of the hinder end of the 

 body, and even regenerate new segments to take the 

 place of those lost. But even when a worm's body is 

 severed very near the anterior end, both pieces are 

 likely to die. 



Annelids are the most efficient animals of worm 

 body plan. They live in the bottom muds of the sea's 

 deepest abysses and in the almost oxygen-free sedi- 

 ments below deep fresh-water lakes. Others inhabit 

 the open surfaces of glaciers high on mountain shoul- 

 ders, and the foliage along jungle paths where passers- 

 by may furnish food. They perform midnight ballets 

 at the dark of the moon in tropical waters, and till 

 the soil in lands where winter's frost reaches far below 

 the surface. 



Annelids form an important part of the diet for 

 many hydroids and anemones, corals and jellyfishes, 

 flatworms and nemerteans, other annelid worms, 

 crustaceans and insects, sea stars and serpent stars, 

 fish, and a host of terrestrial vertebrates. Of the six 

 thousand-odd kinds of living annelids, most swim or 

 build shelters for themselves in the sea. 



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