i6 



FRESH-WATER BIOLOGY 



Nematoda 

 OR True Round- 

 worms 



GORDIACEA 



OR Hair Snakes 



ACANTHOCEPHALA 



OR Thorny- 

 headed Worms 



Trochelminthes 

 or Trochal 

 Worms 



Rotatoria 

 OR Wheel 



Animalcules 



Gastrotricha 



Coelhelminthes 

 (Annelida) 

 or Segmented 

 Worms 



Chaetopoda or 

 Bristle Worms 



HiRUDINEA 



OR Leeches 



Both free and parasitic forms common in all sorts 

 of environments; free-living species most abun- 

 dant in fresh waters and in moist soils; parasitic 

 species common in fresh-water hosts. 



For free-living Nematoda, see Chapter XV, 



page 459- 



For parasitic Nematoda, see Chapter XVI, 



page 510. 

 Parasitic in young life in insects; adult stage free- 

 living in fresh water. 



See Chapter XVI, page 535. 

 Exclusively parasitic, without trace of alimentary 

 system. In many fresh-water hosts. Adults in 

 vertebrates; larval forms imperfectly known, 

 parasitize invertebrates. 



See Chapter XVI, page 542. 

 Among the most characteristic of aquatic or- 

 ganisms. Favorite objects of study with the 

 early microscopists. 



Microscopic free-Uving forms, very rarely para- 

 sitic. Abundant in fresh- water bodies of all sorts; 

 rare in the sea. 



See Chapter XVII, page 553. 

 Minute free-living forms. Abundant in fresh water 

 to which the group is limited. Imperfectly known. 



See Chapter XVIII, page 621. 

 Two classes in fresh water both well represented; 

 other classes exclusively marine. 



One sub-class (Polychaeta) confined to the sea 

 save for rare types in fresh-water bodies near the 

 ocean; the other sub-class (OHgochaeta) found 

 mostly in fresh water and on land. 



See Chapter XIX, page 632. 

 Both free-living and parasitic species, the former 

 mostly in fresh water with a few species also on 

 land in moist regions; rarely marine, as ectopara- 

 sites of fishes. 



See Chapter XX, page 646. 



