Copepods (/ˈkoʊpəpɒd/; meaning "oar-feet") are a group of small crustaceans found in nearly every freshwater and saltwater habitat. Some species are planktonic (inhabiting sea waters), some are benthic (living on the ocean floor), a number of species have parasitic phases, and some continental species may live in limnoterrestrial habitats and other wet terrestrial places. Copepods have an appearance of a flatworm with a 2-sided tail and a huge wide-open mouth.