Protists

Chromista

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The Chromista are a very large and diverse group of organisms. Almost all of the species of the Chromista are photosynthetic (except for the water molds) and aquatic, and almost all fall into the general category of algae. The various groups of the Chromista vary in shape and size from the single celled diatoms to the sometimes huge brown algae (kelp is a famous example). All of the members of the Chromista (except the non-photosynthetic groups) share the possession of the form of chlorophyll known as chorophyll c. Chlorophyll c does not occur in plants or the "green algae". In addition the Chromista groups store energy in the form of varous oils. Green plants store enery in the form of starch.

There are several groups comprising the Chromista. Some of the more well known groups are:

Bacilliarophyta (Diatoms). Diatoms are ubiquitous and occur in abundance in both fresh and marine environments. Fresh water forms are often useful indicators of environmental quality. Most species are single-celled, although a few are weakly colonial.

Silicoflagellata (Silicoflagellates). Silicoflagellates are planktonic marine algae that are both photosynthetic and heterotrophic. They have an internal silica skeletons constructed of a network of bars. Silicoflagellates are much less common than diatoms, but are widely distributed throughout the oceans of the world. Silicoflagellates propel themselves by a long flagellum.

Phaeophyta (Brown Algae). The brown algae are marine and multicelluar and comprise the largest algae of the world. Some species of kelp may be up to 60 meters in length. The brown algae are composed of either branched filaments or leaflike growths called thalli. The brown algae are particularly noteworthy for the differentiation of several different cell types in many cases analagous (but not homologous to the found in plants).

Oomycota (Water Molds). The water molds have traditionally been classified with the fungi and slime molds, but are now generally considered to be non-photosynthetic members of the Chromista.

Prymnesiophyta (Coccolithophores). The Coccolithophores and abundant single-celled marine organisms with a covering of calcareous plates. These organisms are one of the primary producers of limestone.

Testaceafilosea. The Testaceafilosa are a group of amoeboid organisms and are non-photosynthetic. However they have an outer shell (test) of silicon scales and appear to be related to other groups of the Chromista.

Xanthophyta (Yellow-green algae). The Xanthophyta are photosynthetic organisms living primarily in freshwater, though some are found in marine waters, in damp soil, or on tree trunks. Unlike the other Chromista, Xanthophyta completely lack the brown pigment fucoxanthin. Like these other chromists however, they lack the chlorophyll b of plants, and instead have chlorophyll c. This gives them a characteristic yellowish-green color.

Chrysophyta (Golden-brown Algae).

GENERAL

Introduction to the Chromista. University of California Museum of Paleontology. Information on the systematics, biology, and morphology of the Chromista.

Algae: The Forgotten Treasure of Tidepools. F. Perez, C. Kjeldsen, and J. Hughley. A wonderful gallery of photographs of Rhodophyta (red algae), Phaeophyta (brown algae), and Chlorophyta (green algae) from the tidepools of California. The site also has a little information about each group and each of the genera illustrated.

Seaweed. Michael D. Guiry. National University of Ireland. A searchable database of the seaweeds of the North Atlantic. This site also has photographs of seaweeds, and sections on what seaweed are and how they are used by humans. A very nice site.

DIATOMS

The Diatom Collection of the California Academy of Sciences. This site documents the California Academy of Science's diatom collection and is fairly technical. However it does have a tremendous collection of descriptions of photographs of the genera and species of freshwater diatoms.

Center for Algal Microscopy and Image Digitization. R. Lowe and D. Johnson. A large gallery of photographs of diatoms from four localities.

Paleolimnology and Diatom Home Pages. Indiana University. Electron Micrographs of diatoms.

Great Lakes Diatom Home Page. This great site deals with the diatoms of the Great Lakes. It begins with a list of genera, with each genus linked to photographs and information about each species in the genus. Not yet done, but a tremendous source of information and illustrations of diatoms.

Grass of the Sea. GEK, Inc. This commercial site (microscopes) has excellent non-technical introductions to diatoms and dinoflagellates.

Diatoms: Living Snowflakes. Susan Sobehrad. A general introduction to diatoms and their commercial uses.

COCCOLITHOPHORES

Emiliania huxleyi Home Page. Toby Tyrell. A fascinating story about this dominant oceanic coccolithophore with great photographs and other pictures and information about the species.