So, the sea urchin is a small, spiny, globular animal that is related to the star fish. They live in every ocean and are often black or dull shades of green, purple, olive, brown, and red.
Sea urchins have tube feet, which are part of the water vascular system and are seen on the star fish, too. They eat algae and move slowly. Sea otters, wolf eels, and triggerfish prey on the sea urchin. Oddly enough, their gonads are a delicacy in many places!
Anyways, the world urchin is an old name for a hedgehog, so it makes sense that a spiny globular animal in the sea would be named after the hedgehog. Just like the hedgehog, sea urchins use their spines that stick out from their bodies as protection against predators.
They can poke through human skin, too, but they aren’t dangerous. The spines are around one to three centimeters in length. Be careful with sea urchins in the Caribbean, though, because their spines can be anywhere from ten to thirty centimeters long.