Copepoda

Copepoda is a class of small crustaceans within the superclass Multicrustacea, with some classifications instead ranking it a subclass within class Hexanauplia, comprising about 13,000 described species, of which roughly 2,800 live in fresh water. Copepods occupy nearly every marine and freshwater habitat, including planktonic and benthic zones, parasitic forms living on host organisms, and terrestrial wetlands, and typically measure only 1 to 2 millimeters, with a teardrop-shaped body, large antennae and usually a single median compound eye. Planktonic copepods dominate the zooplankton and are a major food source for small fish; scientists have suggested they may form the largest animal biomass on Earth and contribute more to ocean productivity than krill, and possibly more than all other organism groups combined.