A filamentous structure, referred to as a trichome, possesses heterocysts that are consistent in diameter along the entire length of the filament and does not exhibit branching. The heterocysts are either distributed intermittently or situated at the bottom of the trichome. There is a mucous sheath surrounding the trichome, which is nearly transparent or barely visible. Importantly, the heterocysts located at the base of the trichome never develop into large akinetes.