7 6 



COMMUNITIES OF LARGE LAKES 



About a dozen species of crustaceans are common in the lake. They 

 feed chiefly on the protozoa, diatoms, desmids, and possibly the rotifers 

 (85). Such crustaceans constitute almost the sole food of young fishes and 

 are the first food of the young whitefishes (79). They are divided into 

 copepods and Cladocera (and ostracods, rare). This division of the 

 crustaceans is known as the Entomostraca. The smallest and most 



Representative Crustaceans and Rotifers of the Limnetic Community of 



Lake Michigan 



Fig. 15. — A common copepod (Cyclops bicuspidatus); 25 times natural size 

 (after Forbes). 



Fig. 16. — A cladoceran (Bosmina); enlarged (from Forbes after Gerstaecker) . 

 Fig. 17. — A cladoceran (Daphne hyalina galeala); enlarged as indicated (after 

 Smith). 



Fig. 18. — A pelagic rotifer (Notops pelagicus Jen.); 180 times natural size (after 

 Jennings). 



Fig. 19. — The same, side view. 



abundant of the Entomostraca of the lake is only 1 . 1 mm. in length and 

 is slender and colorless. It is the slender Cyclops bicuspidatus, shown 

 in Fig. 15. 



The commonest Cladocera of the lake are Bosmina (Fig. 16), Daphne 

 retrocurva, and Daphne hyalina (Fig. 17). One other small species 

 (Leptodora hyalina) belonging to this group is a very interesting creature. 



