PHYLUM ANNELIDA. SEGMENTED WORMS 



195 



oysters, but other bivalved mollusks may 

 be attacked; also years of low infesta- 

 tion may be followed by years of heavy 

 mortality. 



Sedentary polychaetes are among the more 

 conspicuous agents that cause fouling on the 

 bottoms of ships, dikes, and various harbor 

 installations. They not only cause destruc- 

 tion of the building materials, but add to the 

 submerged weight so that the speed of a 

 vessel is materially lessened. Periodic dv)'- 

 docking of vessels in harbor cities is required 

 to clear the hulls of fouling organisms. 



As reef-building agents, some sand- and 

 lime-concreting, tube-building polychaetes 

 are important in some parts of the world, 

 changing shore contours, building up land 

 masses, and transporting vast amounts of 

 inert materials. As a result of selective ac- 

 tion in the construction of tubes or mat- 

 rices, some reefs or bars are likely to be 

 pure sand or lime particles of homogeneous 

 size. 



Use of certain polychaetes as food, such 

 as the palolo, is of interest since there are 

 certain traditional rites attending such 

 feasts. The annual occurrence of swarms is 

 predictable within narrow limits in certain 

 regions of the south Pacific. Since the por- 

 tions taken consist of almost pure yolk-laden 

 eggs, a highly nutritive food is available. In 

 oriental countries a large echiurid worm is 

 collected, dried, and used as food. 



The widespread occurrence of fireworms 

 (species of the polychaete family Amphino- 

 midae) found along tropical shores is of 

 interest to man largely because of the in- 

 juries that may be inflicted. The worms are 

 sometimes large, as much as a foot long, 

 with striking color patterns and brilliant 

 displays, creeping conspicuously over rocky 

 surfaces. The unwary collector who picks 

 them up is startled by severe burning from 

 the contact. The injuries are produced by 

 the harpoonlike bristles that penetrate hu- 

 man skin. 



The use of the leech (Fig. 105) in medi- 



cine was based on the theory that many 

 illnesses were due to "bad blood," either 

 locally or generally; bloodletting, as the 

 practice is called, was thus considered a cure 

 for many ailments. Today in modern med- 

 ical practice, transfusions of blood into the 

 body are a common procedure, instead of 

 bloodletting, to get rid of "bad blood." How- 

 ever, so common was leeching in olden times 

 that doctors were often called leeches. Not 

 only Hirudo medicinalis but other species 

 were used in various parts of the world. 

 Wordsworth's interesting poem, "The Leech 

 Gatherer" was based on the medicinal use 

 of the leech. Bloodletting by leeches is now 

 extremely rare in this country. In addition 

 to such therapeutic use, the leech has been 

 used as a drug, supposedly, to cure loss or 

 graying of hair and other symptoms of old 

 age. 



Leeches may be very annoying, especially 

 in tropical regions where they live among 

 dense vegetation and may attach themselves 

 in large numbers to human beings and other 

 animals. It has been said that such leeches 

 caused much discomfort to the soldiers of 

 Napoleon when they invaded North Africa. 

 The salivary glands of leeches produce a 

 substance termed hirudin, which prevents 

 clotting of blood while the leech is feeding. 

 For this reason a wound made by a leech 

 may bleed for some time after the leech has 

 detached itself. Hirudin is used in modern 

 medicine as an anticoagulant. 



CLASSIFICATION OF THE 

 PHYLUM ANNELIDA 



{For reference purposes only) 



Phylum Annelida. Annelids are bilaterally 

 symmetrical, segmented worms; the body cavity 

 is a true coelom; the nervous system consists 

 of a dorsal brain and a pair of ventral nerve 

 cords with, topically, a pair of ganglia in each 

 segment; the digestive tract is a straight tube 

 with a mouth that is anterior and ventral, and 



