Protista

The Kingdom Protista refers to all the Eukaryotes except for the Plantae, Fungi, and Animalia. A few (eg kelp) are multicellular and grow to great size, but most are single-celled organisms of great complexity.

Traditionally protists have been divided into the protozoa, which were classed among the animals, the algae, which were classed among the plants, as well as a few forms that were classed among the fungi. These were further divided on the basis of locomotion and pigmentation:

• Flagellates move by means of whip-like flagella, and represent most lines of protists.
• Amoeboids move by means of deformation.
• Sporozoans are entirely parasitic forms that don't move and get around via spores.
• Ciliophora move by many short flagella (called cilia), and have a very complicated structure characterized by two distinct types of nucleus.
• Algae include motile and non-motile forms that have chloroplasts, and so are capable of photosynthesis.
• Oomycota and Slime molds include forms resembling fungi.

Most of these groups are overlapping and polyphyletic, but they are nonetheless a good place to start exploring protist diversity. Protists are ubiquitous in aqueous environments, and though are generally too small to see with the naked eye (usually 10-500 microns), anyone with a light microscope can observe them. A few are important parasites.