Final answer:
The daymark shape used in the lateral system is a triangle.
Step-by-step explanation:
In the lateral system, the daymark shape used is triangle. Daymarks are navigational aids placed on buoys or beacons to assist ship navigators in determining their positions and direction. In the lateral system, the colors and shapes of the daymarks indicate which side of the buoy or beacon should be passed when navigating different channels or waterways.