Cladoceran

From Great Lakes Wiki

Cladoceran, AKA the waterflea is a mircoscopic crustacean that can be used as an indicator species. They are important because they eat a lot of alga, and are a major food source for predators. They are often abundant, a single cubic meter of water can contain millions of these animals.

Image from:www.auburn.edu/~webbeec/limnology/ephippium.htm