CHAPTER X. 



GENERAL ECOLOGY, COMMENSALISM AND 

 PARASITISM. 



As stated in the introductory chapter (p. 25), Protozoa may be 

 found wherever there is moisture. The general distribution is also 

 outlined, particularly with regard to deep sea forms. It is pointed 

 out, furthermore, that fresh water forms, both genera and species, 

 are for the most part cosmopolitan, so that a piece of research 

 begun in New York may be continued on similar forms in Siam, 

 China or Australia. Similar or identical species may be found in 

 both fresh and salt water or brackish water. There are, however, 

 a certain number of ecological centers which permit of a rough 

 classification into: (1) Water-dwelling forms; (2) semi-terrestrial 

 forms; (3) soil-dwelling forms; (4) sapropelic forms; (5) coprozoic 

 forms; and (6) parasitic forms. 



1. Water-dwelling Protozoa.— Without too much exaggeration 

 this caption might well be applied to all Protozoa; here, however, 

 it is limited to those Protozoa which live in ordinary exposed waters, 

 where certain ecological conditions lend themselves to the vital 

 needs of some types and are fatal to others. These needs have to 

 do in the main with food requirements and oxygen pressure and a 

 rough classification, without taxonomic value, was suggested by 

 Kolkwitz in 1908. This was based upon the requirements of 

 water-dwelling forms in respect to the amounts and conditions of 

 organic matter present. Habitat groups were proposed under the 

 terms katharobic, oligosaprobic, mesosaprobic and polysaprobic. 

 Katharobic types are rare, for their environment is fresh water 

 springs, running rivers and streams which are free for the most part 

 of organic matter but rich in oxygen. 



Oligosaprobic types are those which are able to live in waters 

 with little organic matter but rich in mineral matters. The chief 

 types here are the chlorophyll-bearing Protista, but some types of 

 Protozoa also are able to live (Amoeba proteus, Lacrymaria olor, 

 Trachelius sp., Frontonia sp., Ophrydium versatile, etc.). 



Mesosaprobic types are numerically greater than those of other 

 habitat groups, for in this environment active oxidation is going 

 on and organic matter is decomposing. In addition to many 

 algal forms we find here flagellates such as Bodo, Tetramitus, 

 Anthophysa and Peranema, and many common ciliates including 

 Paramecium, Coleps, Spirostomum, Colpoda, Chilodon, Stenfor, 

 Stylonychia, Euplotes, Vorticella, etc. Heliozoa are represented by 

 Actinophrys and Actinosplaerium. 



