Rotifera

Rotifers are a group of microscopic organisms with sizes ranging from .1 to 1 mm in length. Their bodies comprise of three parts: a posterior foot, a trunk containing the internal organs, and an anterior head region which usually has a band of cilia spanning it's circumference, this band is called the corona.
The picture below gives a good example of the variations of body form within the phylum Rotifera.

Rotifer 'A' is an example of a Seisonid rotifer, they use their specially adapted foot to attach themselves to the carapace of crustaceans. Rotifer 'B' is a Bdelloid rotifer, these are either free swimming or creeping animals. The remaining rotifers in the diagram (C-H) are from the class Monogonta, among the wide variety of body forms in this class are free swimming (D-F) as well as sessile (G and H) rotifers.
Evident from the picture above, some of the ciliary structures have been modified into either long bristles, such as in collotheca rotifers or into thicker spike structures. These adaptations are usually for feeding purposes. In other cases, the cilia are reduced significantly.
In terms of the rotiferan life cycle, they rotate between asexual and sexual reproductive strategies. In ideal conditions, there are only females within a population reproducing through parthenogenisis. During extreme conditions, males will be developed and sexual reproduction will produce eggs which can lay dormant until ideal conditions return, starting the cycle over again.