Polytomella Aragão 1910

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.

Polytomella is a genus of green algae in the family Dunaliellaceae. Polytomella is a free-living, flagellated, nonphotosynthetic green alga with a highly reduced, linear fragmented mitochondrial genome. Polytomella, as it exists today, bears evidence of once having a functional photosynthetic plastid which has over evolutionary time changed such that it would appear now to have no genome or gene expressing mechanisms remaining to it. Having transitioned completely to heterotrophy, Polytomella uses organic acids, alcohols and monosaccharides as its carbon source. Despite being an evolutionary descendant of the green algae, Polytomella is a colourless organism because it has lost its photosynthetic ability.