The types of zooplankton according to size are picoplankton, nanoplankton, microplankton, mesoplankton, macroplankton and megaplankton. The types of zooplankton according to stage of development are meroplankton and holoplankton.
Zooplankton are categorized by size and/or stage of development. The types of zooplankton according to size are picoplankton, which measure less than 2 micrometers; nanoplankton, which measure between 2 and 20 micrometers; microplankton, which measure between 20 and 200 micrometers; mesoplankton, which measure between 0.2 and 20 millimeters; macroplankton, which measure between 20 and 200 millimeters; and megaplankton, which measure above 200 millimeters. The types according to developmental stage are meroplankton and holoplankton. Meroplankton are larvae that turn into mollusks, worms, crustaceans or insects, while holoplankton, such as pteropods and chaetognaths, stay as plankton during their whole life cycle. Some of the most common plankton include protists, nanoplanktonic flagellates, cnidarians and ctenophores.
The nanoplanktonic flagellate is a type of zooplankton that helps control bacteria populations. Flagellates have a long tail used for swimming, whereas ciliates have hair-like structures called cilia. Some dinoflagellates use their net-like structure, known as protoplasmic net, to catch prey bigger than bacteria. There are also dinoflagellate species that kill fish and cause red tides. Ciliates usually capture bacteria, other protists and phytoplankton.