How many eyes do sea scallops have?

Scallop is a common name that encompasses various species of marine bivalve mollusks in the taxonomic family "Pectinidae". Scallops have up to 200 small (about 1 mm) eyes arranged along the edge of their mantles. These eyes represent a unique innovation among mollusks, relying on a concave, parabolic mirror of guanine crystals, a highly reflective material that can be seen in everything from fish scales to chameleon skin. They use these crystals to focus and retro-reflect light instead of a lens as found in many other types of eyes. Although these crystals usually form into bulky prisms, the crystals in the scallop's eye are perfect squares that, much like a telescope mirror, create a smooth surface that minimizes optical distortions. Their eyes also possess a double-layered retina, the outer retina responding most strongly to light and the inner to abrupt darkness.

While these many eyes are unable to resolve shapes with high fidelity, the combined sensitivity of both retinas to light entering the eye and light retro-reflected from the mirror grants scallops exceptional contrast definition, as well as the ability to detect changing patterns of light and motion.

Scallops primarily rely on their eyes as an 'early-warning' threat detection system, scanning around them for movement or shadows which could potentially indicate predators.