Class Conjugatophyceae Engl. (1892) see Class Zygnematophyceae Round ex Guiry (2013) Order Zygnematales - filamentous conjugates and saccoderm desmids Family Zygnemataceae (Meneghini) Kützing (1843) Genus Trigonum A.K. Mahato & P. Mahato (1994) [monotypic] Trigonum indicum A.K. Mahato & P. Mahato