A Huge Predator of the Microworld - Bursaria sp.

This Mystery Organism is Bursaria sp., a remarkably large ciliate protozoan found in ponds and lakes. Equipped with a huge oral opening, Bursaria glides and spirals through the water propelled by cilia on its surface. As it travels, it literally gulps in almost any single-celled organism it encounters. In this photo, you can easily see the sickle-shaped ciliated oral groove, and the remnants of both algae and other food digesting in food vacuoles. At .5 - 1 mm, Bursaria is one of the largest ciliates, and it is also among the largest known cells.

To learn more about ciliates, see our program, Branches on the Tree of Life: Protists. For a rich overview of freshwater biology, see our program: The Biology of Lakes, Ponds, Streams and Wetlands.