Closteriopsis

Closteriopsis is a unicellular organism. Cells are 10–240 μm long and 1–6.5 μm wide, and are very long and narrow, either straight or curved with usually pointed tips.^[1] Most sources describe Closteriopsis as lacking a mucilaginous envelope, although it has been documented in one species.^[4] Cells have smooth cell walls, a single nucleus and a central or parietal, ribbon-like chloroplast with multiple pyrenoids arranged in a series. Reproduction occurs asexually by the formation of two to eight autospores, which form in a series and are released through the rupture of the parental cell wall. Flagellated stages and sexual reproduction have not been observed in this genus.^[1]

Closteriopsis is similar to other narrow, spindle-shaped organisms such as Keratococcus, Schroederia and Monoraphidium, and differs from them in having multiple pyrenoids per chloroplast.^[1][4] It is also similar to some acicular species of Closterium (hence the name), from which it is distinguished by having only one chloroplast and reproducing by autospores.^[5] Species are distinguished from each other based on chloroplast morphology and cell size and shape.^[1]