Closterium moniliforme is a diverse genus comprising solitary cells, each consisting of two identical halves known as semicells. While typically microscopic, some species can grow large enough to be visible to the naked eye. The cells are elongated and often crescent-shaped, with rounded, truncated, or pointed poles. The cell surface may appear smooth or feature striations or punctae. Initially transparent, the cell wall can darken over time due to the accumulation of iron and manganese compounds. The cell nucleus is centrally located within the cell. Each semicell contains a single axial chloroplast with several pyrenoids dispersed throughout. At both ends of the cell, there is typically a polar vacuole, often containing prominent barium sulfate crystals.