Light micrograph of a Simocephalus sp. water flea. Water fleas are small crustaceans, commonly found in fresh water. They are filter feeders that ingest algae, protozoa or organic matter, and are a constituent of plankton. This water flea also carries embryos with visible eye-spots under her upper shell. Magnification: x20 when printed at 10 centimetres wide at its longest edge.