Genus Unda Schaeffer, 1926
Diagnosis: Locomotive form as a flattened ovoid with length less than breadth. Length between 20 and 60 µm. Hyaloplasm characteristically advances in waves at anterior margin. No posterior uroid. Floating form with short cylindrical pseudopodia. Nucleus spherical. Cytoplasm often with small vesicles and conspicuous greenish or yellowish granules. No cysts known. Fine structure of surface coat unknown.
Ecology: Marine, with 3 described species.