Hi Nithya!

These are multicellular organisms with well-developed organ systems. The organisims belonging to phylum echinodermata are only marine, these are not found in terrestial or fresh water conditons. And these are found in varoius colors and shapes. These are classified into 5 categories:

1. Asteroidea : They have a flattened, star-shaped body with five arms. they possess tube feet with suckers and respire through papulae. Example : Asterias, Zoroaster.
2. Ophiuroidea : These are flat with pentamerous discs and they do not possess any suckers in tube feet. Respire through bursae. example: Ophiderma, Amphuria.
3. Echinoidea : They are hemispherical in shape with suckers in tube feet. They do not have arms example: Echinus, Cidaris.
4. Holothuroidea : long and cylindrical, respire through the cloacal respiratory tree.And they have suckers. example: Cucumaria, Holothuria.
5. Crinoidea : they are star shaped with no suckers. Example: Neometra, Antedon.

Thankyou!