Sea urchins have been alive for about 300 million years, but they have not changed or undergone any process of evolution in all that time. The fossil shown here is 150 million years old. A marine invertebrate, sea urchins have soft bodies encased in a thin shell covered with the spines that protect them from their enemies. They can move these spines; on some species, they are poisonous and reach a length of 30 centimeters (11.8 in). Tube feet protruding from the bodies of sea urchins adhere to rocks so that they can move comfortably along the ocean floor. Fossil discoveries show that sea urchins have possessed all these characteristics since the first moment they came into being and that they have undergone no change at all throughout that time. The explanation is clear: As with other creatures, sea urchins did not evolve, but were created complete with all their characteristics.