Tetrabaena socialis, a colonial volvocid flagellate. T. socialis was formerly known as Gonium sociale until the monospecific genus Tetrabaena was erected (Nozaki,H. and Itoh, M. J. Phycol. 30:353-365, 1994).The colonies are plate-shaped with four cells all oriented in the same direction. Extracellular matrix joining adjacent cells can be seen. The gelatinous envelope surrounding the whole colony is not seen in these images. The ovoid cells have two equal-length flagella, a small eyespot, large cup-shaped chloroplast and posterior round pyrenoid. From freshwater pond near Boise, Idaho. Oblique illumination. This image was taken by William Bourland. He now uses a Zeiss Axioskop 2 with Spot Insight and Spot Flex CCD cameras (Diagnostic Instruments). Image copyright: William Bourland, image used under license to MBL (micro*scope).
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Freshwater and Terrestrial Microbes of Idaho (USA) and Elsewhere
|Description of Tetrabaena: Colonies plate-shaped, square, with generally 4 cells oriented with their longitudinal axes more or less in the same direction; individual extracellular matrix zone with protuberances forming connections with adjoining cells; cells also held together by fragile gelatinous capsule zone outside tripartite boundary surrounding entire colony; cells ovoid or nearly spherical, with 2 equal flagella; chloroplast single, cup-shaped, with a single (rarely 2) basal pyrenoid(s) and an anterior or nearly median eyespot; contractile vacuoles 2, anterior; asexual reproduction by formation of daughter colony by each cell; sexual reproduction isogamous, homothallic or heterothallic; each cell escaping from its cellular sheath to become a spherical gamete; only one of the two conjugating gametes bearing a mating papilla; zygotes spherical, with a reticulate wall; on germination, 4 biflagellate gone cells liberated separately; nutrition apparently obligately phototrophic; commonly found in freshwater, especially in pools and ponds |