(Rotifera) are microscopic animals with about 1000 cells. Most are around
100-500 um long and are common in freshwater throughout the world with a few saltwater species.
There are about 2000 different species classified into three classes.
is derived from Latin and means "wheel-bearer". They get their name
from the corona at the top of their head, which is composed of several ciliated tufts
around the mouth that, when in motion resemble a wheel.
cilia are used both for locomotion and create a current that sweeps food into the
mouth. Most free-living forms have pairs of posterior toes to anchor themselves while feeding.
There are a variety of different shapes of rotifers. There is a well-developed cuticle which may be rigid, giving the animal a box-like
shape, or flexible, giving the animal a worm-like shape. A few of these move by
inch-worming along the substrate. Other rotifers are sessile, living inside tubes or gelatinous holdfasts, and may even be colonial.
The closest relatives to the rotifers are the Acanthocephala (spiny-headed worms).
Rotifers are very important in
ecological systems because of their high reproductive rates. They play important roles in energy flow and nutrient cycling, accounting for more than 50% of the zooplankton production in some
freshwater environments. Most species are free-living herbivores, bacteriovores or predators.
They, in turn, are fed upon by small fish.