An amoeba and a rhizopod from the Irish Sea. Whereas amoebas are
capable to move by transforming their plasma the rhizopod is limited on
forming subtle filaments. The cell on the right is about 30 Ám in diameter.
By definition all zooplankton are animals that drift freely in the water and feed on organic material. Zooplankton are mobile and most of them are predators. They have representatives in different size categories and nearly all animal clades.