Cosmarium etenoideum is a species of green algae belonging to the desmid group, recognized for its oval to elliptical cell shape with a characteristic figure-eight appearance due to a slight constriction in the middle. Each cell ranges from 30 to 100 micrometers in length and is enclosed in a thick, transparent cellulose cell wall that often exhibits fine ornamentation or striations. Chloroplasts, disk-shaped and located peripherally within the cell, enable photosynthesis. Reproduction occurs both asexually through binary fission and sexually via gamete formation and conjugation to produce zygospores. Found in freshwater environments like ponds, lakes, and slow-moving streams, Cosmarium etenoideum attaches to submerged surfaces and contributes to ecosystem dynamics by oxygen production and as a food source for microorganisms. Non-motile, it remains fixed to substrates or drifts passively in water. Its unique morphology and ecological role highlight its significance in freshwater biology and ecological studies.