The name “urchin” is an old word for hedgehog, which Sea Urchins resemble. Sea Urchins (or just urchins), are spiny, globular animals that inhabit all the Earth’s oceans, from shallow depths to those more than 16,000 ft. The Sea Urchin’s shell (also known as a “test”) is round and spiny, typically from 1.2 to 3.9 inches across. The test reveals a five-fold symmetry not easily recognizable before its spines are removed. Common colors include black and dull shades of green, olive, brown, purple, blue, and red.