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Description of Platydorina

Colonies flattened, slightly twisted, more or less horseshoe-shaped, of 16 to 32 cells arranged in one layer in a common gelatinous matrix; colonial boundary rounded anteriorly, posteriorly extended into 3-5 rounded projections; each cell surrounded by separate fibrillar zone (cellular envelope) of extracellular matrix within tripartite colonial boundary; cells separated from each other by spaces, in 16-celled colonies 12 cells arranged marginally and 4 in the middle, in 32-celled colonies, 16 cells arranged marginally and 16 cells in the middle (the latter in 4 tiers); cells spherical to ovoid, all of same size, bearing 2 equal apical flagella; chloroplast cup-shaped, longitudinally striated; usually with 1 pyrenoid; eyespot present; nucleus more or less central; 2 contractile vacuoles, anterior; asexual reproduction potentially by each cell of a colony, with a plakeal stage and inversion to form a daughter colony; sexual reproduction anisogamous, heterothallic, with large, biflagellate female gametes (eggs) and packets of small, biflagellate male gametes (sperm); zygotes spherical, smooth-walled; on germination, a single biflagellate gone cell escaping from zygote wall and dividing into a gone colony; nutrition phototrophic or photo-organotrophic; in freshwater pools, ponds, lakes and rivers, so far recorded from North and South America only.




Source: BioPedia

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