Daphnia pulex, or water flea, belongs to the cladoceran group of micro_crustaceans. They vary greatly in size, but most measure less than 1 mm in length. They possess a single compound eye and a pair of branched antennae which are used in locomotion. Despite their small size, they are an important food source for fish and larger crustaceans due to their vast numbers. Recorded under Rheinberg illumination.