Pictured in this week’s AquaNerd POTW is a gorgeous Tridacna derasa clam. The T. derasa clam is the second largest of the giant clam species, reaching up to two feet long. This species has a very narrow byssal opening unlike T. maxima and T. crocea clams which are far more abundant in the aquarium trade. Because of this narrow opening, Derasa clams do not rely on a foot or byssal threads to anchor it to a hard surface. Instead, they rely on their weight to keep them stationary over softer substrates, though they can use their feet to reposition themselves.