Architectonica maxima, or the giant sundial, is a large, low-spired sea snail known for its flattened, broad, and thick shell, which can range from 19–82 mm in size. Key features include a distinctive spiral groove on the shoulder slope, a beaded surface with axial lines that form a checkered pattern and a basic cream colour with brown spots. The species is found on sandy and muddy substrates in the Indo-Pacific and is the largest member of the sundial family (Architectonicidae).