The Stone Sea Urchin (Echinostrephus acanthocercus or Echinothrix spp.) is a robust marine invertebrate known for its hard, stone-like shell and formidable spines. It features a dense, spiny exterior that provides protection from predators and helps it anchor securely to the substrate. The color of the Stone Sea Urchin can vary, often ranging from dark brown to gray or even purple, with a surface covered in short, sharp spines.