PARASITISM 327 



Phylum Trochelminthes. These comprise the rotifers 

 or wheel animalcules, and are rarely parasitic. 



Class Rotifera. Of these a few species are 

 parasitic in Crustacea. 



Phylum Annulate. Of the segmented worms few are 

 parasitic. 



Class Archi-annelida. These embrace a num- 

 ber of parasitic forms, none of which infests 

 man. 



Class Discophora. These embrace the leeches 

 which may be included among the occasional or 

 optional parasites. They live by attaching 

 themselves to fishes and sometimes to warm 

 blooded animals, sucking blood until distended, 

 then letting go again. They are parasitic in 

 the same manner as bed-bugs and fleas. 

 Phylum Mollusca. Of the mollusks very 

 few are parasitic. 



Class Gasteropoda. Of these Eulima, Stylifer, 

 and Thyca are parasitic in Holothurians, 

 star-fishes, and Echinoids, embedding them- 

 selves in the skin where their presence occasions 

 growths resembling tumors. 



Phylum Arthropoda. This is a phylum rich in para- 

 sitic forms of great interest. 

 Class Crustacea : 



Entomostraca. These include the water 

 fleas or Copepods of which many are 

 parasitic. Argulus is an epiparasite of 

 fishes, boring between their scales; Caligus 

 is parasitic upon the gills of fishes; Lera- 

 conema an endoparasite of the muscle of 

 fishes. These parasites are very harm- 

 ful to their respective hosts. 

 Another group, of which the barnacles, the 

 Cirripedia, are well-known members, fur- 

 nish a few parasitic forms that attach 

 themselves to the abdomens of crabs. 



