144 



POND COMMUNITIES 



crustaceans constitute an important element in this association. The 

 smaller amphipod (Hyalella knickerbockeri) is abundant among the 

 chara. The crayfish (Cambarus immunis) occurs here sparingly. In 

 ponds there is an important element of small crustaceans that belong 

 to the vegetation and the bottom; this element is composed chiefly of 



Representatives of the Submerged Vegetation Association 



Figs. 89, 90, 91. — Larva of a midge (89), pupa of the same (90), the adult. 

 Midges are inhabitants of the chara-covered bottom; enlarged about 4 times (after 

 Johannsen, Bull. N.Y. State Museum). 



Fig. 92. — The eggs of the common large black horsefly on the tip of the bulrush 



stalk. 



Fig. 93. — The chara-inhabiting caddis-worm (Leptocerinae); enlarged as indi- 

 cated. 



Fig. 94. — Ostracod (Notodromas monacha Miill.); 30 times natural size (after 

 Sharp) . 



Ostracoda (Fig. 94), which are small bivalved forms resembling the 

 bivalved Mollusca. They form food for fishes to a small degree. 



Especially abundant just under the chara are the red water-mites 

 (Limnochares aquaticus) (Fig. 80, p. 130). One sees numbers of these 



