The body of the rotifer is externally but not internally segmented. The body is telescopic, with a semi-flexible, extendible, transparent cuticle covering. It is the cuticle that suggests rotifers are close relatives of roundworms and arthropods. Within the body are the stomach and reproductive organs. As rotifers are microscopic animals, their diet must consist of matter small enough to fit through their tiny mouths during filter feeding.
Rotifers are primarily omnivorous, but some species have been known to be cannibalistic.
The diet of rotifers most commonly consists of dead or decomposing organic materials, as well as unicellular algae and other phytoplankton that are primary producers in aquatic communities. Such feeding habits make some rotifers primary consumers. Rotifers are in turn prey to carnivorous secondary consumers, including shrimp and crabs. As well as their morphology and feeding habits, reproduction in rotifers is rather unusual. Several types of reproduction have been observed in rotifers.