I've posted pictures of rotifers before (here) but they are such amazing animals that there's always room for another - especially this one, which looks like a monster from a sci-fi horror movie. I found it at the edge of a pond today and it is - I think - a species of Euchlanis, which belongs to a group called loricate rotifers. A lorica is a hard outer shell (the word lorica is Latin for 'body armour') that provides protection and maybe has hydrodynamic properties that aid swimming. The protective function is evident in this photograph (above), where the animal's head is withdrawn into its shield-shaped lorica, which has claw-like points guarding either side of the opening. The animal is about a fifth of a millimetre long.
It may be that the shield-shaped lorica also functions like a wing, generating lift as the animal swims through the water, powered by a tuft of fast-beating cilia at the head end- which you can see beating in the short video below. When at rest the animal can anchor itself with its tail spines, which open and close like a pair of scissors.
These images were taken with differential interference contrast optics, which generate an apparent three-dimensional image of microscopic objects.
You can find out more about rotifers here.