Iceberg Clam

Though technically neither an iceberg nor clam, the devastating elemental known as an iceberg clam has earned its appropriate name from its natural camouflage and feeding tendencies. This spherical ambush predator exhibits full thermal control over the water that surrounds and comprises its mutable form, luring tired swimmers and adrift vessels with the promise of reprieve before enveloping and boiling them alive.

Unless it has eaten recently enough to still be digesting its meal, a melted iceberg clam is nearly imperceptible in a large body of water. Since it's not expending energy to maintain its frozen exterior, it can wait weeks or even months before feeding again, riding ocean currents until some unlucky creature or vessel next enters its body—and never leaves.