Polytomella (paul-ee-toe-mell-a) is one of a small number of green (Viridaeplantae) algal genera which lack plastids. There are four flagella inserting in a square pattern - and only two opposed flagella can be seen in this image. The flagella insert in small dimples at the anterior end of the cell. Often found in habitats rich in organic matter and low in oxygen. Phase contrast. This picture was taken by David Patterson, Linda Amaral Zettler and Virginia Edgcomb of material from the salt marsh at Little Sippewissett (Massachusetts, USA) in Autumn, 2000 and in Spring and summer, 2001. Image copyright: D. J. Patterson, L. Amaral-Zettler and V. Edgcomb, image used under license to MBL (micro*scope).
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From the collection
Little Sippewissett salt marsh, Massachusetts, USA
|Description of Polytomella: Cells colourless, with leucoplasts; cell wall absent; cells ellipsoidal, inverted ovoid or pear-shaped, or nearly spherical; 4 equal flagella; leucoplast(s) highly reticulate and branched, starch grains usually many, located peripherally in the posterior two-thirds of the cell; pyrenoid absent; eyespot present or absent; nucleus centrally located or anteriorly displaced; contractile vacuoles 2 or 4, anteriorly located; Golgi bodies perinuclear; asexual reproduction by longitudinal division of vegetative flagellate cells; cysts spherical with four-layered, thick cell wall; upon excystment each cyst releases a single, flagellate vegetative cell; sexual reproduction isogamous to form a quadriflagellate planozygote that produces four progeny cells by two perpendicularly oriented cell divisions; nutrition heterotrophic, able to grow on acetate but not on glucose; relatively rare in freshwater, found among rotting vegetation. |