daphniaEnglishOxford New American Dictionarydaphnia /ˈdafnēə, ˈdæfniə / ▸ noun (plural same) a tiny and semitransparent freshwater crustacean with long antennae and prominent eyes, often used as food for aquarium fish. Also called water flea. Genus Daphnia, order Cladocera. – ORIGIN modern Latin, from Greek Daphnē, from the name of the nymph Daphne.