The marine zooplankton community is a vast and diverse group of organisms which drift on ocean currents.  Zooplankton are divided into two main groups: the holoplankton (true plankton) and the meroplankton (larval stages).

Mixed Holoplankton

Mixed Meroplankton

Holoplankton are zooplankton that remain in the plankton all their lives.  They do not grow or change into anything else.  This groups includes; copepods, thecosomes, hyperiids, euphausiids,tunicates, isopods and some jellies.

Meroplankton are the eggs, juvenile and larval stages of other marine organisms such as fish, barnacles, hydroids, polychetes, crabs, shrimp and starfish. 

Having a planktonic larval stage aids dispersal of young organisms so they can colonise new areas of the ocean.