Phylum Echinodermata are marine organisms. While the adults are radially symmetrical the larvae remain bilaterally symmetrical. The mouth is on the lower surface. The Echinodermata is a phylum containing some 13,000 extinct and 7,000 extant species. They have a water vascular system with tube feet. eg. star fishes, brittle stars, sea urchins and sea-cucumbers.
Living representatives are only found in marine environment, making the phylum the largest lacking terrestrial and fresh water forms.
Phylum Chordata are phylum derives its name from one of the common characteristics of this group namely the notochord (Gr. noton, back + L. chorda, cord). The animals belonging to all other phyla of the Animal Kingdom are often termed ‘the non -chordates’ or ‘the invertebrates’ since they have neither notochord nor backbone in their body. The backboned animals (vertebrates), together with a few closely re-lated animals which do not possess a backbone, are included in this phylum. Most of the living chordates are familiar vertebrate animals. The chordates are of primary interest because human beings are members of this group.