Also found in: Dictionary, Thesaurus, Medical, Wikipedia.
a phylum of lower plants (algae). The plants are microscopic and usually mobile (with two or, less frequently, one flagellum in one or two intersecting grooves). They may be unicellular, colonial, or less frequently, filamentous. The majority are either naked or have a casing in the form of a carapace of two halves, formed of angular plates. The brown chloroplasts contain chlorophyll a, chlorophyll b, and brown pigments. The storage product is starch or, less commonly, oil. The nucleus is primitive. Some species have a pigment spot, a contractile vacuole, and, sometimes, a cytopharynx.
The Pyrrophyta include autotrophs and heterotrophs with a saprophytic, parasitic, or holozoic type of nutrition. Some are symbionts of coelenterates and radiolarians. Mobile species reproduce by division; nonmobile forms multiply by spores and zoospores. Sexual reproduction, or isogamy, is rarely observed.
Pyrrophyta live in freshwaters and seas. They serve as food for invertebrates and sometimes cause water bloom and the destruction of fish.
The phylum has two subphyla, Cryptophytina and Dinophytina, which zoologists assign to the order Dinoflagellata. There are approximately 125 genera, including more than 1,000 species. The USSR has about 50 genera, embracing 500 species. On the basis of morphological and biochemical characteristics, the plants are often considered as two phyla: Cryptophyta and Dinophyta.
REFERENCEKiselev, I. A. Pirofitovye vodorosli. Moscow, 1954. (Opredelitel’ presnowdnykh vodoroslei SSSR, issue 6.)
IU. E. PETROV