sea urchin

A sea urchin is a small, round marine animal covered with spines, belonging to the echinoderm family like starfish and sea cucumbers. It moves slowly along the ocean floor using tube feet that extend through its shell. Its body is encased in a hard, often colorful shell called a test, which has holes for its feet and mouthparts. Sea urchins are herbivores, primarily grazing on algae and coral. They play an important role in marine ecosystems by controlling algae growth, but can become problematic in overpopulation, damaging underwater habitats.