Colony of rotifers (Conochilus hippocrepis). 100x magnification. Darkfield mciroscopy.

 Rotifers are tiny animals known for the characteristic crown of cilia (little hair-like structures) spinning around their heads, helping them suck in food particles. Each individual is made up of about 1,000 cells and has a brain and nervous system, stomach and digestive system, reproductive organs and bladder, but no circulatory system. C. hippocrepis is a member of one of only two families of colonial rotifers. There are three colonies in this photograph, each with dozens of individual animals.