Tridacna clams have hundreds of 'eyes' along the edges
of their siphonal tissue or 'mantle'.
As well as detecting
shadows to warn the clam of potential predators,
these eyes are sensitive to green, blue, and
ultraviolet light.
This helps the Tridacna clam to better position itself toward
sunlight
to expose as much zooxanthellae algae as possible.
Zooxanthellae transform
carbon dioxide and dissolved nitrogen into
carbohydrates, glucose and amino acids for their
host clam.
With sufficient sunlight, zooxanthellae can provide
all of the
respiratory carbon requirements of a Tridacna clam.
