Copepods

Copepods are a group of small crustaceans found in the sea and nearly every freshwater habitat. Many species are planktonic, but more are benthic, and some continental species may live in limno-terrestrial habitats and other wet terrestrial places, such as swamps, under leaf fall in wet forests, bogs, springs, ephemeral ponds and puddles, damp moss, or water-filled recesses (phytothelmata) of plants such as bromeliads and pitcher plants. Many live underground in marine and freshwater caves, sinkholes, or stream beds. Some copepods are parasitic and attach themselves to fish, sharks, marine mammals, and many kinds of invertebrates such as molluscs, tunicates, or corals.
Copepods form a subclass belonging to the subphylum Crustacea (crustaceans). Some authors consider the copepods to be a full class. The group contains ten orders with some 14,000 described species. A scientist that studies copepods is a copepodologist.