Echinoderms are economically important to humans due to their use in scientific research and education and also for food. Scientists have learned much about animal reproduction, fertilization and development by studying sea urchins, sea stars and other echinoderms.
Scientists have used echinoderms to study fertilization due to the fact that many species are easy to cultivate in a lab setting and also because they produce a huge amount of eggs at one time. Echinoderm eggs are also the reason these animals are economically important for food, as sea urchin roe is considered a delicacy in many places and is commonly served in sushi restaurants around the world.
There are approximately 7,000 known species of echinoderms, which can be found in every ocean on the planet. In addition, scientists have identified more than 13,000 extinct species of echinoderms through fossil records. Nearly all known species live in seas and oceans, although there are a few species that live in brackish coastal waters. The phylum Echinodermata is the largest group to include only marine animals, as there are no known freshwater or terrestrial species.
The name echinoderm comes from the ancient Greek term for spiny skin, and many echinoderms are covered in spines. All echinoderms share the characteristic of radial symmetry, which means their limbs or appendages all grow out from one identical center point.