76 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 
Fic. 15.—A common copepod (Cyclops bicuspidatus); 25 times natural size 
(after Forbes). 
Fic. 16.—A cladoceran (Bosmina); enlarged (from Forbes after Gerstaecker). 
Fic. 17.—A cladoceran (Daphne hyalina galeata); enlarged as indicated (after 
Smith). 
Fic. 18.—A pelagic rotifer (Notops pelagicus Jen.); 180 times natural size (after 
Jennings). 
Fic. 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 
im Big. 1x5. 
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. 
