Heterocyst and Hormogonium

Heterocysts:-

Heterocysts are specialized nitrogen-fixing cells, produced by some filamentous cyanobacteria, which form during nitrogen starvation conditions. These specialized cells do not possess functioning photosynthetic apparatus because their primary function is the anaerobic fixation of atmospheric nitrogen.

Hormogonia:-

Hormogonia is a fraction of a filament in algae that detaches from the organism and reproduces by cell division. Hormogonia are found in cyanobacteria such as Nostoc. They are produced during vegetative reproduction in unicellular and filamentous cyanobacteria.