Katodinium asymmetricum cells are ovoid from the ventral side, slightly obliquely dorso-ventrally flattened, approximately 12 microns long, epicone approximately 10 microns wide, hypocone approximately 5 microns wide. Possessing fine thecal plates, plate pattern not established. Epicone dome shaped, 0.6 0.7 of the total cell length, with a notch just to the left of the apex. Cingulum very wide, initially descending, and slightly displaced. Sulcus narrow, on the right side of the hypocone, and turning to the left as it descends towards the anterior end. Longitudinal flagellum arises at the anterior end of the sulcus. Nucleus is in the left half of the cell, about 4 microns diameter. Chloroplasts absent. Food particles occasionally present.
