Distinguishing features of organisms in the Phylum Echinodermata include a lack of body segmentation, radial symmetry and life adaptations for marine environments. The Phylum Echinodermata includes more than 6,000 different species. Most organisms in this category take the form of starfish and have endoskeletons, which appear in humans, too, and give organisms the ability to move and grow.
Of all the phyla in the animal kingdom, the Phylum Echinodermata most closely resembles the Phylum Chordata, which includes humans. Echinoderms, like humans, have distinct spinal columns. They have coeloms deriving from digestive tubes, which resembles the internal digestive system of humans and many animals. Like people, organisms in the Phylum Echinodermata contain endoskeletons that form primarily from hard, dense calcium carbonate. Sharp spikes radiate out from the skeletons of echinoderms, giving them a distinct appearance.
In addition to starfish, this phylum includes other aquatic species too, such as sea cucumbers, brittle stars and sand dollars. While some, like starfish, contain projecting arms, others have a pentameral design. This design features a body symmetry of five equally sized parts. Echinoderms derive nutrients and water through a water-vascular system. This system involves a network of internal canals that breaks into smaller channels internally, culminating in tube feet. A feature unique to echinoderms is the ability to regenerate organs and limbs upon damage or loss.