Pyrrophyta is a botanical division which is composed of marine organisms known as "fire algae". These algae get their common name because most of them are red in color. Fire algae are an important component of ocean plankton. The major class within this division is Class Dinophyceae, the dinoflagellates.

Members of the dinoflagellate genus Gonyaulax produce a neurotoxin. An overabundance of these organisms may cause an algal bloom that is poisonous to fish and other organisms, including humans who eat shellfish that have accumulated the algal toxins in their flesh. The fabled red tides are caused by Gonyaulax blooms.

Other dinoflagellate species are bioluminescent. If you've ever seen nighttime waves that seem to glow as they hit the rocks, you're seeing the action of fire algae.

There are over 1100 species in this division. Members of Pyrrophyta are single-celled, photosynthetic organisms that move via two flagella. They store their food as starch, and their cell walls are made of cellulose. They usually reproduce asexually.