The echinodermata are known as the spiny skinned animal. They bear spines which play an important role in protection. The name echinodermata was introduced by Jacob Klein. Leuchart put these organisms into separate phyla. They arise from the three germ layers such as ectoderm, mesoderm and endoderm. They are known as triploblastic animals. They have unisexual and bisexual forms and show sexual dimorphism. They have bilateral symmetry in larvae and in adults they show a pentamerous radial symmetry. They have an organ system level of organization. The digestive system is complete and has mouth and anus for ingestion and egestion. They have no asexual reproduction forms. They have the epidermis layer which is single layered and have muscles which are smooth and occur beneath the dermis. The respiration occurs through the peristomnial gills, papulae, genital bruise and cloacal respiratory tree. They are present in the different organisms. They are mainly marine and live at the bottom of sea. They move slowly. They can be free or attached to the substratum. Their body is of different shapes like star, cylindrical etc. They lack head and are unsegmented. They have a true body cavity known as enterocoelic coelom. There is a unique feature of this phylum known as a water vascular system. In this a perforated plate is present which allows the water to move in and out of the system. They have no blood vascular system but have haemal and perihaemal system. So the circulatory system is of open type and has no respiratory pigment and heart. They have no special organs for the excretion. They have a nitrogenous waste which comes out through the gill. The chief excretory waste is ammonia. The nervous system is made up of nerve rings and nerve cords which are radial in nature. Their sense organs are not fully formed. They have an external mode of fertilization. The process of autotomy and the regeneration is quite marked. Their development is indirect and forms a larvae which metamorphise to form an adult. The adults are radial symmetrical while the larvae are bilateral symmetrical.
The echinodermata resemble the chordates as they have an endoskeleton made up of mesoderm. Their mouth is derived from ectoderm. The process of gastrulation occurs by invagination. The anus is formed from blastopore. They are dueterostomes. The cleavage of egg is radial and indeterminate. They have enterocoelous coelom. This very much proves that chordates rise from echinodermata.