Prostoma ruhrum (Leidy) 

 (Stichostemma ruhrum (Leidy) ) 

 Mouth without a proboscis and situated somewhat back fiom the anterior 

 end, frequently in the middle of the ventral side; digestive tract modi' 

 fied saC'like; size various; color various 



PLATYHELMINTHES— Turbenarm Flatworms 

 3. Body segmented 



ANNELIDA Annelids 

 Body not segmented 



NEMATHELMINTHES Round Worms 



KEY TO THE COMMON NEMATHELMINTHES OR 

 ROUND WORMS 



1. Usually minute forms living in soil, on vegetation, etc.; intestine com' 



plete (Very difficult to identify. The genera are not included here.) 

 Class l^lematoda Thread Worms or Nemas 

 Parasitic, usually in insects, as young; freediving as adults; getting to be 

 several inches long; digestive tract often somewhat degenerate in the 

 adult 2. 



2. Cuticle usually finely striate; posterior end pointed; digestive tract usually 



degenerate posteriorly; frecliving in water, soil or on vegetation 

 Family Mermithidae of Class J\lematoda 



Mermis Dujardin (typical genus) "Cabbage Worms" 

 Cuticle usually rugose; posterior end split or bluntly rounded; digestive 

 tract often degenerate anteriorly; free-living in water — Class Gordi' 

 acea Hair Worms 3. 



3. Anterior end rounded, usually with a narrow, dark ring just back from 



the tip; posterior end rounded (in female) or split into two tips (in 

 male) 



Gordius Linn. 

 Anterior end oblique or pointed; posterior end rounded or split into two 

 or three tips 4. 



4. Anterior end oblique, with a wide, dark ring just back from the tip; pos' 



terior end split into two (in male) or three (in female) tips 



Paragordius Camerano 

 Anterior end pointed, without a dark ring; posterior end not split, but 

 rounded (somewhat coiled in male, swollen in female) 



Chordodes Creplin 



THE FREE-LIVING FLATWORMS OR TURBELLARIA 



L Intestine simple, modified sac-like, sometimes dividing into many small 

 branches; animals usually minute (Keyed mainly on internal charac' 

 ters and very difficult to identify. The genera are not included in 

 this key.) 



Order Rhabdocoelida Smaller Water Turbellaria 



82 



