Sea Urchin

Sea urchins are spiny ocean life. The shell of a sea urchin, which biologists call the test, is globular in shape, and covered with spines. The size of the test in adult sea urchins is typically in the range of 3 to 10 cm (1-4 in.).

Sea urchin pictures - purple sea urchin

What does a sea urchin get its name?

The name Sea Urchin comes from their resemblance to hedgehogs, hedgehog being one meaning of the word "urchin".

Facts on the sea urchin 

Typical sea urchins have spines 1-2 cm (approximately 1/2 to 1 in.) in length, a millimeter or two thick, and not terribly sharp. Some sea urchins are purple sea urchin, green sea urchin, and red sea urchin. Pictures of purple sea urchins are shown below.

Sea urchin pictures - purple sea urchin

Anatomy of a sea urchin

Sea urchins are echinoderms, which also includes starfish, sea cucumbers, Brittle stars, and crinoids. Sea urchins have five-fold symmetry (called pentamerism) and move by means of hundreds of tiny, transparent, adhesive "tube feet".