The order Echinidermata is divided into five classes.
1. Asteroids: Their bodies are star-shaped with five arms. Tube fit exists. Spines and pedicilli are present on the body. For example – sea star (Asterias vulgaris).
2. Ophuroidea: Their bodies are pentamerous discs. Tube fit and spine present on the body. Their arms are long. For example – Cucumaria (Cucumaria planci).
3. Echinoidea: Their bodies are hemispherical. Tube fit exists. The body has no arms. Spine present. For example, sea urchin (Echinus esculentus).
4. Holothuroids: Their bodies are long cylindrical in shape. The body has no arms, spines and pedicellariae. But tube fit exists. For example, sea cucumber (Holothuria impatiens).
5. Crinoid: Their bodies are star-shaped. The body does not have tube feet, spines, pedicillaries etc.