KEY TO ANIMAL PARASITES 



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CLASSIFICATION OF PHYLA OF IMPORTANCE IN ANIMAL PARASITOLOGY 

 (According to Stiles) 



1. Unicellular animals, as the parasites of malaria Protozoa. 



Pluricellular animals; metazoa 2 



2. Body more or less flattened dorsoventrally 4 



Body ordinarily round in transverse section 



3. Body never annulated, never provided with legs; no jaws present 5 



Body annulated, or at least provided with mouth parts; usually breathe through 



a tracheal system; adults with jointed legs 7 



4. Intestine, but no anus, present; one or two suckers present; body not seg- 



mented; parasitic in liver, lungs, blood, intestine; occasionally elsewhere; 

 flukes Trematoda. 



Intestine absent; two or four suckers on head; body of adults segmented; tissue 

 usually contains calcareous corpuscles; adults (tapeworms) parasitic in intes- 

 tine; larvae (bladder worms) parasitic elsewhere Cestoda. 



Intestine and anus present; ventral sucker on posterior end; body annulated like 

 an earthworm; parasitic in upper air-passages, or externally, leeches, blood- 

 suckers Hirudinei. 



5. Intestine absent; armed rostellum present; very rare in man, in intestine, thorn- 



headed worms Acanthocephali. 



Intestine present; no armed rostellum 6 



6. Intestine rudimentary in adult; rare, accidental parasites in intestine of man, hair 



snakes or horse-hair worms Gordiacea. 



Intestine present; parasitic in intestine, muscles, lymphatics, etc., very common 

 and important; roundworms Nematoda. 



7. Six legs present in adult; wings present in most species; larvae annulated much like 



an earthworm; breathe through tracheae; adults ectoparasites; occasionally 

 larva is parasitic under skin, or in wounds, or an accidental parasite in the 

 intestine; insects Insecta. 



Eight legs present in adult, six legs in larva; head and abdomen coalesced; 

 ectoparasites; some burrow under the skin or live in the hair follicles; 

 acarines Acarina. 



Four claws around the mouth; larva encysted in various organs; adult occasion- 

 ally parasitic in nasal passages; tongue worms Linguatulidae. 



Numerous legs present; occasionally accidental parasites in nasal passages or 

 intestine, thousand leggers Myriapoda. 



There are certain terms employed in animal parasitology which it is 

 necessary to understand. Among these we shall refer to the following: 



1. True Parasitism. By this is understood the condition where the parasite does 

 harm to the host, deriving all the benefit of the association. A good example of this 

 would be the hookworm infecting man or animals. 



2. Mutualism. In such an association there is mutual benefit to each party of the 

 association. An instance of this would be the presence of colon bacilli in the intes- 

 tines. The bacillus is furnished a suitable habitat and in return protects its host 

 against strictly pathogenic bacteria. 



