The sea urchin, or nicknamed the "sea hedgehog" are tiny sea animals that are found all over the world in any ocean. Common colors of the sea urchin include black, and dull shades of green, olive, brown, purple, blue, and red. These little guys move slowly, consuming mostly algae, yet are consumed by sea otters, sea stars, wolf eels, triggerfish, and many others.
Walk, Bounce, or Roll?
Like sea cucumbers, sea urchins use tube feet that arise from the five ambulacral grooves on its body. These tube feet are also moved by the water vascular system, which again allows the sea urchin to pump water in and out of the tube feet, which enables them to move. During the larval stage of its life, the urchin builds its spicules, which are sharp crystalline "bones" that consist of its endoskeleton. The spines on the urchin protect it from some predators. It causes a painful wound when contacted by human skin, and can cause serious problems if it is not removed right away. However the numbers tell you that they are not immensely sharp, with a length of 1 to 3 cm and a width of 1 to 2 mm. When in the Caribbean, one should look out for a particular urchin whose spines can reach up to 30 cm long (almost one whole foot!).