A sea urchin is a small, spiny marine animal found on ocean floors around the world. They belong to the class Echinoidea and have a hard shell called a test, which is covered in sharp spines. Sea urchins play a vital role in their ecosystems by grazing on algae, helping to maintain the balance of marine environments.
These creatures are often found in rocky areas and can vary in color, including purple, green, and black. Sea urchins are also known for their edible roe, which is considered a delicacy in many cultures, particularly in Japanese cuisine.