19. Sea Urchin
The sea urchin is well-known for its spiky exterior, which can appear threatening but primarily serves as a defense mechanism. These echinoderms play a crucial role in marine ecosystems by grazing on algae, which helps prevent overgrowth on coral reefs. While their spines can cause discomfort if touched, sea urchins are generally passive creatures. Their ecological importance underscores the delicate balance they help maintain in oceanic environments.