1 66 



Aquatic Organisms 



Macrobiotus may be met in the same way and place, 

 but less commonly. It may also be taken in plancton ; 

 but its favorite habitat appears to be tangles of water- 

 plants, over whose stems it crawls clumsily with the aid 



of its four pairs of stub- 

 by strong-clawed feet. 

 It also inhabits the 

 most temporary pools, 

 even rainspouts and 

 stove urns, and is able 

 to withstand dessi- 

 cation. 



Chastonotus is probably 

 most nearly related to 

 the Rotifers; Macro- 

 biotus, to the mites. 



Bryozoans — The 

 Bryozoans or "moss 

 animals" (called also 

 Polyzoans) are colonial 

 forms that are very 

 common in fresh water. 

 They grow always in 

 sessile colonies, which 

 have a more or less 

 plant-like mode of 

 branching . Their fixity 

 in place, their spreading 

 branches and the 

 brownish color of the 

 test they secrete give 

 the commoner forms 

 an aspect enough like minute brown creeping water 

 mosses to have suggested the name. The individ- 

 ual animals (zooids) of a colony are minute, requir- 

 ing a pocket lens for their examination, but the colo- 



FlG. 76. Bryozoan colonies, slightly en- 

 larged; a dense colony of Plumatella on 

 a grass-stem; a beginning colony on a 

 leaf (above) ; and a loosely grown colony 

 of FredericeUa. 



