protoctist family - any of the families of Protoctista

order Zygnemales, order Zygnematales, Zygnemales, Zygnematales - pond scums; desmids

genus Zygnema, Zygnema - type genus of the family Zygnemataceae

pond scum - free-floating freshwater green algae

genus Spirogyra - a genus of protoctista