Giant Clams are colourful creatures that have hundreds of simple eyes along the edges of their mantle.

The Tridacnid’s eyes are visible as dark spots along the mantle

The largest species of Giant Clam, the Tridacna, are the largest bivalves ever to have existed in the fossil record.
Like all other clams, these fascinating animals are placed in the Phylum Mollusca, along with snails and cephalopods. Within this phylum, the Tridacnids are part of the Class Bivalvia (two valves or halves), which also includes oysters and scallops.
The vast majority of these Bivalves are filter-feeders, which use specialized dual-purpose gills to capture tiny food particles from seawater.

Tridacnid Clams however also acquire nutrition through the harboring of internal algal symbionts. Just as reef-building corals do, the tridacnids maintain populations of single-celled zooxanthellae in parts of their bodies.
These single-celled photosynthetic algae live in the tissues of a host clam within a specialized system of tubes, and when given enough sunlight, they produce far more food than they need for themselves. The extra food (in the form of carbon and energy-packed glucose) is then given to the clam host.

Another fact makes Tridacnid Clams outstandingly special compared to other Bivalves:
They are the only ones that have eyes along the edges of their siphonal tissue or also called mantle.
These eyes are used mostly to detect shadows, which warn the clam of potential predators.
Furthermore, they are also sensitive to green, blue, and ultraviolet light. This helps the clam to position itself toward the light to expose as much zooxanthellae as possible.
This also leads to the assumption that the eyes may also function to detect excessive amounts of potentially harmful UV wavelengths.

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