desmids A group of green algae (division Chlorophyta) which are basically unicellular but have two distinct halves, or ‘semicells’. The cells are usually solitary but in a few species they may form irregular or filamentous colonies. The cells may vary in shape within a single species, making identification and classification difficult. Sexual reproduction occurs by conjugation, similar to that in Spirogyra. They are found mainly in freshwater habitats and are usually indicators of clean (unpolluted) water.

desmids Unicellular green algae of the class Desmidioideae. Like Spirogyra, they have an elaborate chloroplast. The cells of desmids are characteristically split into two halves joined by a narrow neck, each half being a mirror image of the other. The outer wall of the cell is patterned with various protuberances and covered with a mucilaginous sheath, which is thought to play a role in the cell's slow gliding movement. Desmids are found mainly in fresh water.