Polarised light micrograph of a Daphnia sp. water flea with resting eggs. Daphnia are crustaceans found in various aquatic environments such as swamps, lakes and ponds. Resting eggs have a protective case called the ephippium which protects eggs from cold, drought or lack of food. Resting eggs hatch when environmental conditions are more favourable. Daphnia are commonly known as water fleas because their movement resembles that of terrestrial fleas. Dark field illumination. Magnification: x7 when printed at 10 centimetres wide.