Eucampia zodiacus exhibits a trapezoid outline with a valve face that appears concave when viewed in broad girdle view. Cells are linked together in helical chains, connected by costate ocelli located at the tips of the horns on the valve margin. The apertures between adjacent cells vary widely in width and can have angular, elliptical, or square shapes. A single labiate process is situated within the depression in the center of the valve. The cells contain numerous small elliptical chloroplasts.