Marine life individuals per square meter and accounting for about 80% of all individual animals on earth, their diversity of life cycles, and their presence at various trophic levels point at an important role in many ecosystems. Echinoderms (Greek for "spiny skin") is a phylum which contains only marine invertebrates. The adults are recognizable by their radial symmetry (usually five-point) and include starfish, sea urchins, sand dollars, and sea cucumbers, as well as the sea lilies. Echinoderms are found at every ocean depth, from the intertidal zone to the abyssal zone. The phylum contains about 7000 living species, making it the second-largest
Starfish Devonian and late Permian, the blastoids were wiped out and only a few species of crinoids survived. Many starfish species also became extinct in these events, but afterwards the surviving few species diversified rapidly within about sixty million years during the Early Jurassic and the beginning of the Middle Jurassic. A 2012 study found that speciation in starfish can occur rapidly. During the last 6,000 years, divergence in the larval development of "Cryptasterina hystera" and "Cryptasterina pentagona" has taken place, the former adopting internal fertilization and brooding and the latter remaining a broadcast spawner. The scientific name Asteroidea was given