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 µm 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.