Protisten

What are protists?

Because it’s easier to use illustrations instead of words, the pictures above show representatives of this complex group of organisms. They all have in common that they need water to live in. Most of them are very small and it requires a microscope to discover them. In the banner we see from left to right: testate amoebae, a green alga, a red alga and a golden alga.

In former times a taxonomical kingdom named "Protists" or "Protoctists" existed, including all unicellar organized organsims with nuclei, see "Five Kingdoms" by Lynn Margulis and Karlene Schwartz, New York 1982. Nowadays the term "protist" is used only informal and comprises unicellar organized organsims with (Eukaryotes) and without nuclei (Prokaryotes), see Biodiversity and Earth History" by Jens Boenigk, Sabina Wodniok and Edvard Glücksman, Berlin 2015.

A few characteristics of protists are:

- The organization of protists is mostly unicellar or in chains of cells without functional differenciation.

- In the case of eukaryote protists their cells have organelles e. g. for feeding, all kinds of metabolism, osmoregulation and probably defense.

- They have cell sizes between a few micrometers (some flagellates) to some millimeters (e. g. Spirostomum species, a ciliate).

- The multicellular organized protist groups of brown and red algae and some species of slime moulds may reach sizes of up to several square meters.

Different to animals and higher plants protists have no sexual reproduction with embryogenesis. But, the cells of eukaryotic protists also have a cell nucleus which controls vegetative and generative life processes.

For a detailed taxonomic overview look at EOL, a project of Smithsonian Institute called "Encyclopedia of Life".