Rotifer

Rotifers are a type of microscopic, planktonic organism found in freshwater and brackish ecosystems all over the word. Their name comes from a Neo-Latin word meaning “wheel-bearer,” due to the distinctive crown of cilia used for swimming and feeding that look like rotating wheels. These zooplankton have short lifespans of about two weeks are composed of only about 1,000 cells. They’re no larger than a grain of sand yet they have complex bodies with a brain, muscles, and digestive, nervous, and reproductive systems. 

There are more than 2000 known species of rotifers, divided into three classes, Monogononta, Bdelloidea, and Seisonidea. Rotifers play an outsized role in the aquatic ecosystems, consuming bacteria and algae at the base of the food chain and serving as prey for zooplankton and larval fish.