Photographer: © 2014-2016 Dave Waselle · All Rights Reserved.
Tridacna Clam | Palau, Micronesia
There are very old black and white movies that show a diver accidently stepping on one of these and the clam closing on the divers leg trapping him underwater. That has never happened and probably never will. You can see from this photo the mass of flesh composing the body of the animal and they can barely close with there own muscle in the way let alone a diver.
Tridacna Clams are a very unique animal. They have a type of primitive electric eye device that senses light. In this case, several. They sense a quick change of light, like a hand casting a shadow over the shell, and close immediately for their own protection. The mantle also contains transparent cells which focus light into the animals tissue inside the shell. This contributes to forming algae which lives in symbiosis with the clam and that algae disposes of waste and provides the life-giving oxygen to the clam.
They lay on the bottom blending right in with all the corals and other animals making up the coral reef. They also come in numerous colors. This one, to me, looks like Picasso painted one of those dripping farm fields to go with his watches.