Phylum Echinodermata: [Echino-Spiny, Derm-Skin]

• This group is comprised of spiny skinned animals.
• Habit and Habitat: they are free-living, exclusively marine animals that live in groups.
• Symmetry: they are radially symmetric, star-like.
• Body cavity: true coelomic cavity present.
• Body differentiation: They are multicellular, real developed organs are present.
• Germ layer: They are triploploblastic animals.
• Body organization: Body lacks head, but has oral and aboral surface. Oral surface is the side of radially symmetric organisms where mouth is located and aboral is the opposite side of oral surface.
• Skeleton:  Exoskeleton is made up of spiny, hard structures called as ossicles made up of calcium carbonate. Calcareous endoskeleton is also present.
• Life processes:

1. Alimentary canal/ digestive tract is simple. Anus is absent in some of the echinoderms.
2. Body cavity is modified to form water driven vascular system that help in respiration, circulation and locomotion [through tube feet].
3. Excretion organs are absent.
4. They are unisexual. Reproduction is sexual or asexual [regeneration].

Examples:

Starfish [Asterias], Sea urchins [Echinus], sea cucumber [Holothuria], Feather star [Antedon] etc.