|Colonial rotifers from a lake in Germany|
Rotifera comes from the Greek for "wheel bearer," and reflects one of the common names: wheel animals. This rather unusual-sounding common name comes from the ciliated corona that surrounds the mouth and is used to capture food. Due to cilia action, the corona appear to rotate like wheels when viewed under a microscope. There are approximately 1850 species known, with the vast majority of those species being found in freshwater. These animals are actually a common sight in pond water samples, especially those with a fair amount of debris. Samples of lake and pond average between forty and five hundred rotifers per liter. Most rotifers are free living, with parasitism being unusual in this phylum. Though some species are colonial, most are not. They aren't long-lived animals, with five weeks being an unusually long lifespan and one or two weeks being more typical.
|The mastax is seen in the middle left|
Rotifers were one part of the former Phylum Aschelminthes which has since been broken down into several smaller groups. One characteristics that almost all of the aschelminths share is a developmental trait known as eutely. Eutely is when cells stop dividing at a certain point in development and any further growth in the size of the animal happens because the cells that are present increase in size.
|Looping movement in some rotifers|
The cementing substance that is secreted by the toes can also be used in the form of movement seen at left, where a combination of muscular contractions and attachment at the toes will draw the animal across a surface. This method is often called looping due to the body's resemblance to a U-shaped loop. This form of movement does not require swimming via the corona.
|A member of Class Bdelloidea|
Source is Biology of the Invertebrates. Images are from Wikimedia Commons and are under Creative Commons licenses or copyright free: one, two, three, four.