Type of vertebrates including, among others, such animals as starfishes, brittle stars, sea urchins and sea cucumbers. There exist five classes of echinoderms: sea lilies (class Crinoidea), starfishes (class Asteroidea), brittle stars (class Ophiuroidea), sea urchins (class Echinoidea), and sea cucumbers (class Hollothurioidea).

Characteristics of echinoderms are: five-rayed body symmetry and a water-vacsular system used in locomotion. Excretion, respiration and sensory perception. Echinoderms have a respiratory system but respiratory organs are not well developed or even nonexistent. They have a very primitive nervous system and they completely lack separate excretory organs. Starfishes and sea urchins have their moth openings directed upwards, whereas see lilies have it directed downwards. Echinoderms have an internal skeleton formed of solid calcite plates with osscides or spikes protruding above the body surface. The sexes in echinoderms are separate.