Plancton 301 



shelled animals tumbling indecorously about. Some- 

 times almost every female will be carrying a single large 

 egg. Several larger limnetic rotifers, such as Triarthra, 

 Polyarthra and Pedalion, bear conspicuous appendages 

 by which they may be easily recognized. The softer- 

 bodied Synchaeta will be recognized by the pair of ear- 

 like prominences at the front. Other common limnetic 

 forms are shown at 2 (Rotifer neptunius), 21 and 25 of 

 figure 181. 



The Crustacea of fresh-water plancton are its largest 

 organisms. They are its greatest consumers of vege- 

 table products. They are themselves its greatest con- 

 tribution to the food of fishes. Most of them are 

 herbivorous, a few eat a mixed diet of algae and of the 

 smaller animals. The large and powerful Leptodora is 

 strictly carnivorous. The following are the more 

 truly limnetic forms : 



I. Cladocerans ; species of 



Daphne (fig. 234) Diaphanosoma 



Chydorus Ceriodaphnia (fig. 165) 



Bosmina (fig. 91) Polyphemus 



Sida Bythotrephes 



Acroperus (fig. 182) Leptodora. (fig. 186) 



II. Copepods; species of 



Cyclops Epischura 



Diaptomus Limnocalanus 



Canthocamptus (see figures 95 and 96) 



Of plancton animals other than those of the groups 

 above discussed, there are no limnetic forms of any 

 great importance. There is one crustacean of the 

 Malacostracan group, My sis relicta, that occurs in the 

 deeper waters of the great lakes. There is one trans- 

 parent water-mite, A tax crassipes, with unusually long 



