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yellow-green algae[′yel·ō ¦grēn ′al·jē]
(Xanthophyta, also Heterocontae), a division (phylum) of plants. They are unicellular, colonial, or multicellular organisms, free-swimming or sessile, with yello wish-green chromatophores containing, besides chlorophyll, a large quantity of yellow pigments— xanthophyll and β-carotene. They are found chiefly in fresh water and sometimes in soil and sea water. The majority of yellow-green algae are autotrophic organisms that synthesize oils, volutin, and other substances; some of the yellow-green algae are heterotrophic organisms, and a few are holozoic. Some unicellular yellow-green algae are motile and have pulsating vacuoles and eyelets and usually two flagella of different length and structure (hence the second name— Heterocontae). The cells of the yellow-green algae are mononuclear, more rarely polynuclear, and are often surrounded by a hard sheath of two halves containing principally pectin. Yellow-green algae reproduce by binary fission, zoospores, and nonmotile spores. The sexual process, isogamy, is known in only two genera. Spores and cysts are the resting forms. In the USSR, 82 genera (344 species) of freshwater yellow-green algae are known.
IU. E. PETROV