298 Animal Biology 



Life Histories of a Few Representative Nematodes 

 (Unsegmented Roundworms) 



parasite 



ADULT stages 



immature stages 



Human or Pig Roundworm 



(Ascaris lumbricoides) 

 Human Pinworm 



(Enterobius vermicularis) 

 American Hookworm 



(Necator americanus) 

 European Hookworm 



(Ancylostoma duodenale) 

 Elephantiasis (Filarial) 

 Worm 



(Wuchereria bancrofti) 

 Guinea (Filarial) Worm or 

 "Fiery Serpent" 



(Dracunculus medinensis) 

 Pork Roundworm or 

 Trichina 



(Trichinella spiralis) 

 Bird Gapeworm 



(Syngamus trachea) 



Human Whipworm 



(Trichuris trichiura) 

 Common Garden Nematode 



Heterodera [Caconema] 



radicicola) 

 Vinegar "eel" 



(Turbatrix [Anguillula] 



aceti) 



Man, pig 



Man (intestine, cecum) 



Man (skin, intestine, 

 heart, lungs, trachea) 



Man (skin, intestine, 

 heart, lungs, trachea) 



Man (blood stream, 

 lymph, lungs, skin) 



Man (beneath skin) 

 Man (intestine, muscles) 



Fowls, wild birds 



(trachea) (cause of 

 gapes ) 



Man (cecum, appendix) 



Hundreds of plants, 



crops, trees, etc. 



(especially in roots) 

 Vinegar 



Soil, water, pig, man 

 (lung) 



Soil (moist) 

 Soil (moist) 

 Mosquito 



Fresh-water crusta- 

 cean (Cyclops), 

 water 



Pig, rat, cat, dog, 

 flesh-eating animals 



Soil, earthworms 



Soil 



end. Because of the wheel-like movements of these cilia, the animals are com- 

 monly called rotifers or wheel animalcules. The body is somewhat cylindrical, 

 bilaterally symmetrical, and covered with a transparent cuticle. The latter is 

 divided into sections which may be telescoped into each other when the animal 

 contracts. The movements of a pair of chitinous, chewing jaws (mastax) dis- 

 tinguish the living rotifers. A cavity (probably not a true coelom) contains the 

 alimentary canal and a pair of excretory tubes which empty their wastes into a 

 bladder which contracts at intervals, expelling them through the anus (cloacal 

 opening). A forked posterior tail ("foot") is provided with pedal (cement) 

 glands for adhesion. Certain rotifers may resist drying for years and be carried 

 by dust particles in their dried state. Hence, rotifers are among the most widely 

 distributed of animals. Different species of rotifers vary in shape from the free- 

 swimming spheroid forms that float near the surface to the wormlike bottom 

 dwellers or the flowerlike attached types. In certain species, several individuals 

 are grouped in a colony. Some species dwell in tubes of materials made from 

 their surroundings. The life cycles are quite complicated. Three types of eggs 

 are produced : ( 1 ) large, thin-shelled summer eggs which develop parthenogeni- 

 cally (without fertilization) into females, (2) small, thin-shelled summer eggs 

 which develop parthenogenically into males, and (3) thick-shelled winter eggs 

 which when fertilized develop into females. The winter eggs may remain alive 

 in a dormant state for years, developing when suitable conditions occur. Number 

 of species of Rotifers, 1,000. 



