Coelosphaerium kuetzingianum is a colonial planktonic cyanobacterium in the family Merismopediaceae, named in honour of the nineteenth-century German phycologist Friedrich Traugott Kützing, who made foundational contributions to the study of algae and cyanobacteria. The species forms spherical to globular mucilaginous colonies with cells arranged near the periphery of a clear gelatinous matrix—the characteristic architecture of the genus. Individual cells are small, typically 2–5 micrometres in diameter, and possess gas vesicles that confer buoyancy regulation, enabling the organism to position itself advantageously in stratified water columns. Coelosphaerium kuetzingianum has been recorded from freshwater lakes, reservoirs, and ponds across temperate northern Europe, including Denmark, Norway, and Sweden, as well as from Taiwan, indicating a broad latitudinal tolerance. Its occurrence in both boreal and subtropical settings suggests morphological plasticity or the presence of distinct ecotypes within the species concept. As with other members of the genus, it participates in aquatic food webs as a primary producer and is consumed by filter-feeding zooplankton such as cladocerans and rotifers. Eutrophication resulting from agricultural nutrient loading can stimulate cyanobacterial growth in affected water bodies. No IUCN conservation assessment has been undertaken for this planktonic cyanobacterium.