Phylum Annelida and Other IVormlike Coelomates 463 



and is highly branched. There are nine or ten segmentally arranged 

 testes and paired ovaries. 



While many leeches are free-living, feeding on insect larvae and 

 v^orms which they find in the muddy bottoms of streams and lakes, 

 others are parasitic on vertebrates such as turtles and fish. They 

 rasp holes by means of their teeth and jaws in the soft portions of the 

 vertebrate body and suck the blood. This is stored and slowly di- 

 gested in the much-branched crop. 



One common species of leech, Hirudo medicinalis, the medicinal 

 leech, is used even at present in some parts of the world to remove 

 blood from bruises and clots. Leeches are able to keep blood flowing 

 and to prevent its clotting by a substance in their saliva known as 

 hirudin. Hirudin is a powerful anticoagulant and has been used in 

 'medical practice to dissolve emboli and other blood clots. 



In the southeast of Asia and the East Indies, the land leeches 

 occur in tremendous numbers in the tropical rain forests. Here they 

 attack any passing warm-blooded animal including man. Travelers 

 have reported that the leeches are poised on leaves, heads raised, wait- 

 ing to attach any unwary passerby. Others have spoken of the man- 

 ner in which the leeches converge from all directions to the prospective 

 meal. These leeches can stretch to considerable length, becoming very 

 thin. Thus they can pass through tiny openings in clothes and inflict 

 their wounds. Once the leech is engorged it falls to the ground, but 

 the wound continues to bleed due to the presence of the hirudin in the 

 blood. 



OTHER EUCOELOMATES RELATED TO THE ANNELIDA 



The members of the phyla Echiuroidea and Sipunculoidea are both 

 wormlike forms whose further relationship to the Annelids is demon- 

 strated by their possession of a true coelom and a modified trochophore 

 larva. Both, however, are sufficiently different from the annelids to 

 merit being placed in different phyla. 



The Phylum Echiuroidea.— The members of this phylum (Fig. 

 151, D) are entirely marine forms. They have cylindrical, saclike bodies 

 and a long, often spoon-shaped, extensible proboscis. Most are small, 

 but one dwelling off the coast of Japan attains a length of nearly 6 

 feet. 



The adult worms are unsegmented, without parapodia, but with 

 ventral setae. The digestive tract is complete with an anterior mouth 



