mutated from oysters.
Clackers are rubbery, oozy masses living within two hard calcified plates connected by ligaments. These two plates are controlled by a very strong adductor muscle, allowing the creature to open or close them at will. The size and shape of their shells vary from creature to creature. Some are triangular in shape, while others are ovaloid or circular. Some have ridges while others are smooth. Many are symmetrical, while many others are not.
On average, they grow between six and twelve inches in length and weigh a pound or so. The largest known specimen to have known existed grew to be roughly four feet in length, and weighed over five hundred pounds.
Clackers get their name from their hunting behavior. They will quickly open and close their shells, creating vibrations in the water and producing a clicking noise if exposed to air. The vibrations in the water and the clicking noise in the air attracts prey. While they usually root themselves in one spot for long periods of time, clackers do have the ability to move, thanks to a specialized organ connected to their lungs that resembles a pipe. The open their shells, stick the organ out of it and blow air and water out of it, giving them locomotion. In smaller specimens, they are able to propel themselves through the water, while in larger species, they roll and shuffle on the sea bottom.
These shelled creatures can be found across the northeast, from Cape Cod in Massachusetts to Norfolk in Virginia, with the largest concentrations being found in the Long Island Sound, Raritan Bay, Delaware Bay and Chesapeake Bay.
Clackers are primarily opportunistic detritus consumers. Because of the relative ease to find it, and the general abundance of it in the various seas that clackers live in, they consume aquatic vegetation such as loose seaweed and algae. When they have the ability to, clackers consume living creatures, which provide them more nutrients. Depending on their size and location, they can consume fish, crustaceans, insects, birds, and small mammals.
The adductor muscle of clackers is highly developed and is extremely strong. Though the creatures don't hunt, per se, if threatened they can clamp down on threats they deem too close. The clamping of their shells produces a great deal of force. While, in smaller species, the PSI produces might only cause an annoying pinch, in larger species, the pressure produced in larger species can break bones and sever limbs.
When threatened, clackers simply shut their shells. Not only are the calcified plates extremely hard, making it unlikely that predators break them open, but many specimens have grown spikey nubs on them, to deter predators from attacking them in the first place.