Abstract
Lemnicola hungarica (Grunow) Round & Basson taken from brackish and freshwater environments in Southern Brazil was studied for its ultra-structure details, plastid morphology, and ecology. Previously undescribed details are given: a ring of elongated areolae on the mantle of L. hungarica and its plate-like plastid that lies on the araphid valve where it reaches the valve margin and curves itself towards the raphid valve. Lemnicola hungarica thrives in truly freshwater conditions where conductivity values are below 300 μS/cm, and where floating plants are also present.