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Phacotus
Phacotus crassus
Scientific classification
Domain:	Eukaryota
Supergroup:	Archaeplastida
Clade:	Viridiplantae
Division:	Chlorophyta
Class:	Chlorophyceae
Order:	Chlamydomonadales
Family:	Phacotaceae
Genus:	Phacotus Perty
Type species
Phacotus lenticularis (Ehrenberg) Diesing
Species
Phacotus lenticularis Phacotus sphaericus

Phacotus is a genus of green algae in the family Phacotaceae.^[1] It is found in freshwater, and can be plentiful in temperate hardwater lakes.^[2]

Phacotus is a single-celled, uninucleate, motile organism in which the protoplast is contained with a rigid shell, termed a lorica.^[3] The lorica is strongly compressed, colorless to brownish, and consists of two equal parts attached together. The lorica may be smooth, slightly rough or ornamented. The lorica is made of a mixture of carbohydrates, proteins, sulfates, and various minerals including calcite. Under cross-polarized light, the lorica displays two slightly different appearances; one of these may occasionally feature a red ring near the perimeter.^[2] This difference could represent the outer and inner views of the loricae, as they typically separate after the organism's death.^[2]

The protoplast is slightly smaller than the lorica. The chloroplast is cup-shaped, parietal, with an anterior stigma and a pyrenoid. The two flagella emerge from a single opening or two openings within the lorica. Two contractile vacuoles are present at the base of the flagella.^[3]

Asexual reproduction occurs via the formation of two, four, eight or 16 zoospores. The zoospores develop within a gelatinous sporangium, which expands after the two shells of the lorica separate. Sexual reproduction has been reported and is isogamous, but rare.^[4]