Water flea egg case. Coloured scanning electron micrograph (SEM) of an egg case from a Daphnia hrbaceki water flea, surrounded by the ephippium. 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. This specimen measures 0.8mm long.