Closterium is a desmid, a microscopic green algae that occurs in all types of freshwater habitats. Desmids are typically one-celled, though sometimes filamentous or colonial, and are divided symmetrically into semicells connected at a central point. Closterium is characterized by a sickle shape and sometimes contains gypsum crystals.
Source: Closterium Video No. 1
Source: Closterium Tables, XXVII, XXVIII, XXIX, XXX
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