Motile stage: Unicellular; oblate spheroid; average length, 8.1  μm (range 7.1-9.1  μm), average width, 5.6 pm (range 5.0-6.4  μm); thecal vesicles present, no thecal plate; epicone rounded to slightly conical; hypocone, rounded to slightly conical with distinct flange projecting over sulcus from left side; cingulum wide, displaced one times its width; sulcus deep, narrower than cingulum, anterior end at hypocone flange, posterior end at antapex; longitudinal flagellum length 1.5 times body length; chloroplasts peripheral; thylakoids contain three lamellae; major light-harvesting pigment peridinin; two or more stalked pyrenoids penetrated by several thylakoid lamellae; typical dinokaryon nucleus; no trichocysts or stigma; swimming behavior characterized by darting motion with rapid changes in direction.
Non-motile symbiotic stage: Oblate spheroid more tapered than motile stage; length 8-12 pm, width 4-5  μm; no flagella; cingulum and sulcus not evident.