Water flea egg shell. Coloured scanning electron micrograph (SEM) of the surface of the ephippium surrounding eggs from a Chydorus sphaericus water flea subfossil. Water fleas (order Cladocera) are small crustaceans, commonly found in fresh water. Winter, or dry-season, cladoceran eggs have an extra shell layer, the ephippium, that protects them from harsh environmental conditions until they become more favourable. Subfossils are animal remains that have not yet become fully fossilised. Magnification: x830, when printed 10 centimetres wide.