Animated coloured scanning electron micrograph (SEM) of Marine calanoid copepod (Euchaeta sp.). Euchaeta is a genus of the calanoid copepods in the family Euchaetidae (order Calanoida). Calanoida is an order of copepods that can live in both marine and freshwater. Calanoid copepods are dominant in the plankton in many parts of the world's oceans (55%-95% of plankton). They are very important in the aquatic food chain. Commercial fish are dependent on calanoid copepods (larval or adult forms).