Protists are relatively simple, unicellular eukaryotic organisms that are distinct from animals, plants, and fungi yet similar enough that protists are believed to have paved the way for the evolution of early plants, animals, and fungi.

 

Protists, of which about 200,000 species have been named, were historically considered to form their own kingdom, Protista, but are now regarded as a loose grouping of 30 or 40 disparate phyla. They fall into three major categories (or four if the slime molds and water molds are counted separately):

 

• Animal-like protists called protozoa
• Planet-like protists called algae
• Fungi-like protists called slime molds and water molds

 

Animal-like protists

These are the protozoa and include the following phyla:

 

• Ciliophora (cilia bearing protists), e.g. paramecium
• Sporozoa, e.g. plasmodia
• Sarcodina (protists with false feet), e.g. amoeba

 

Plant-like protists

These include the single-celled and colonial algae.

 

Fungi-like protists

These include the slime molds (plasmodial and cellular varieties) and the water molds.