Marine invertebrates 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 grouping of deuterostomes (a superphylum), after the chordates (which include the vertebrates, such as birds, fishes, mammals, and reptiles). Echinoderms are unique among
Ferreira's spiny tree-rat in 1817, Anselme Gaëtan Desmarest described the species based on this specimen housed in the National Museum of Natural History (France) of Paris. Using ancient DNA technology, a portion of the mitochondrial cytochrome b gene has been sequenced from a small skin fragment of this holotype. DNA sequence comparisons then suggested that the specimen was originally obtained in eastern Amazonia north of the Amazon River, most likely in the Brazilian state of Amapá. Ferreira's spiny tree-rat Ferreira's spiny tree-rat, "Mesomys hispidus", is a spiny rat species from South America. It is found in Bolivia, Brazil, Colombia, Ecuador, French Guiana, Guyana,