Keratella rotifer. Darkfield illuminated light micrograph of a Keratella sp. rotifer (centre) on sphagnum sp. moss. This footless rotifer possesses a protective shell, or lorica, and is surprisingly complex on the inside. It has a brain, reproductive organs, a bladder and a digestive system. It is omnivorous, eating bacteria, debris or small protozoans. Magnification: x200 when printed 10 centimetres wide.