The Alveolates are a very recently recognized group. Detailed studies of the internal structure of these protists demonstrates that they all share a system of sacs underneath their cell membranes. These closely packed sacs are called alveoli.
Alveoplates include some of the most familiar and numerous protist groups, including the Ciliata, or ciliates, such as Paramecium and Stentor. The ciliates are the most diverse group of heterotrophic protists, with 7000 species.
Also very diverse, though not as familiar, are the Foraminifera. While the average person may not be familiar with this group, they are very well known to paleontologists, who use their fossils to date rocks, determine paleoclimate, and search for oil deposits.
A third group is the dinoflagellates. These alveolates are photosynthetic, able to manufacture their own food from sunlight, carbon dioxide, and sufficient dissolved nutrients. The dinoflagellates are best known for their periodic population booms that result in "red tides" that may kill fish and shellfish.
A final group of Alveolates are the Apicomplexa, a group of parasitic and disease-causing protists. They are known for having some of the most complex life cycles among single-celled creatures.
For additional information:
Visit the Alveolates page on the Tree of Life for current information on systematics of this group.