Phylum Echinodermata :-

Phylum Echinodermata :- These are marine organisms. While the adults are radially symmetrical the larvae remain bilaterally symmetrical. The mouth is on the lower surface. They have a  water vascular system with  tube feet. eg. star fishes, brittle stars, sea urchins and sea-cucumbers. Phylum Chordata This 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.

Diversity of Chordates

The chordates exhibit an astonishing diversity in form, physiology and habits. The number of chordate species is limited. About 49,000 species are on record which are only half of the living species of molluscs and less than one tenth of arthropods. Despite their modest number of species, the chor- dates make remarkable contribution to the bio-mass of the earth. Nearly all of them are medium to large in size. The vertebrates in particular are consider- ably larger and many of them are among the largest of living animals. The gigantic blue whale which is 35 meters long and 120 tons in weight is the biggest known animal. The smallest vertebrate ,  philippine goby is a fish,

measuring only 10 mm in length. The chordates are able to occupy various kinds of habitats. They have adapted themselves to more modes of existence than any other group. They are found in the sea, in freshwater, in the air and on all parts of land from the poles to the equator.

General Characters : The three distinctive characteristics of the chordates are the presence of  notochord, dorsal tubular nerve cord and pharyngeal gill slits.