Copepods

This group gathers Crustaceans subcategory members belonging to the subclass Copepoda, tiny, often nearly transparent crustaceans that, despite measuring only a millimeter or two in most species, are thought to make up the single largest source of animal protein in the world's oceans by sheer combined biomass, forming a foundational link near the base of marine and freshwater food webs everywhere. Most copepods swim with a distinctive, jerky, hopping motion powered by long antennae and specialized swimming legs, and free-living species graze on microscopic phytoplankton, while a considerable number of copepod species have instead evolved a parasitic lifestyle, attaching to the gills, skin or fins of fish and other marine animals. Their enormous numbers make copepods a critical food source for fish larvae, small fish, and even some of the largest animals on Earth, several species of baleen whale included.