rotifer, also called wheel animalcule, any of the approximately 2,000 species of microscopic, aquatic invertebrates that constitute the phylum Rotifera. Rotifers are so named because the circular arrangement of moving cilia (tiny hairlike structures) at the front end resembles a rotating wheel.

Figure 33.3 C. 1: Rotifers: A bdelloid rotifer is a member of a class of rotifers found in fresh water and moist soil. The rotifer body consists of a head, a truck, and a foot. They eat by filtering food into the mouth by creating currents with the corona. The rotifer body form consists of a head (which contains the corona), a trunk (which.