The purpose of this page is to present the physical characteristics of rotifers. Rotifera (rota=wheel, -fera=those that bear) range in size from 40 µm to 3 mm but most are between 100-500 µm. There are three orders (or classes) of rotifers and they include: the Seisonacea-epizoic marine rotifers,

the Bdelloidea-swimming, or creeping rotifer with two germovitellaria (germovitellaria are combined ovaries and yolk glands), and the Monogononta swimming or sessile forms with single germovitellaria. The Bdelloidea are also known as Digononta. The body of the rotifer consists of three parts, the head that bears a ciliated corona, a trunk, and a posterior tail or foot. Many species of rotifers are able to withstand long dry periods.  Rotifers are found in activated sludge with a long mean cell residence time.  They are important because of their ability to consume bacteria and alga.  Rotifers graze on the surface of flocs consuming bacteria that are more exposed to the environment and thus less healthy. By keeping the populations of bacteria and alga in check, rotifers are an important part of the treatment process.