32 LEECHES 



Other Piscicolidae which may be mentioned are Piscicola 

 (Fig. 17) a parasite of freshwater fishes, Pontohdella (Fig. 19) which 

 attacks marine fishes, particularly elasmobranchs, and Ahranchus 

 which has been found on shore fishes round many parts of the 

 North Atlantic. Our knowledge of marine fish parasites is very 

 fragmentary, owing to the difficulty of obtaining material. 



4. Gnathobdellae 



Turning to the Gnathobdellae, the jawed leeches, there is little 

 to be said about the anatomy of members of the family Hirudidae, 

 since Hirudo, a typical and widespread form, has been fully 

 described. Although Hirudo has been introduced to North 

 America, the most common blood-sucking parasite of mammals 

 in that country is Macrohdella decora. In India and adjacent 

 countries Hirudidae abound in swamps, rice fields, etc., and 

 there are several abundant forms, including Hirudo and Hirudin- 

 aria, which pierce the skin of the body or limbs, and Limnatis 

 which enters the mouth of men and animals while drinking. Some 

 members of this family such as Haemopis have weak jaws and 

 blunt teeth and have abandoned the blood sucking habit in favour 

 of a carnivorous mode of life. Haemopis sanguisuga of Europe and 

 Haemopis marmoratis of North America are typical examples. They 

 spend a good deal of their time out of water and feed on earth- 

 worms, insects, molluscs, or decaying flesh of any kind. The crop 

 has lost most of its diverticula and Haemopis resembles in this the 

 members of the family Erpobdellidae. 



The outstanding characteristic of the Haemadipsidae is that 

 they have become better adapted to terrestrial life than any other 

 kind of leech. They are blood-sucking forms which attack man 

 and animals, lurking on vegetation in damp places. They are 

 particularly abundant in South East Asia. One of the chief prob- 

 lems confronting leeches on land is the need to keep the sucker 

 sufficiently moist to enable it to function properly. The Haemadip- 

 sidae have achieved this by arranging that the first pair of nephridia 

 open onto the anterior sucker and the last pair open onto mem- 

 branous folds of the posterior body wall, the auricles, which are in 



