Submariner — Sea Life

The Rivetmaw Siege Crab is what happens when a trench predator learns to wear wreckage as armor. Its shell is layered with pressure-warped plates, porthole rings, old bolts, and dead steel it has fused into living carapace. It advances slowly until the last possible second, then brings its crusher claw down with the blunt certainty of a depth charge. Military crews prize intact Siege Crab plating because it absorbs impact instead of merely deflecting it. Mounted as a hull component, the plates bleed force away through thousands of tiny stress channels. The trick is removing them before the crab decides the submarine has better armor than it does.