Echinoderms are spiny-skinned, exclusively marine, organisms whose bodies can usually be divided into five parts around a central axis. They possess calcareous plates or ossicles, ambulacra (food) grooves and a water vascular system with tube feet. Paleontologists recognize many extinct classes within this phylum. There are five extant (living) classes within the Echinodermata:

• The Asteroidea (starfish)
• Crinoidea (crinoids)
• Ophiuroidea (brittle stars)
• Echinoidea (sea urchins)
• Holothuroidea (sea cucumbers)

 - Crinoids

Vertebrates
 - Mammals
 - Dinosaurs & Birds
 - Reptiles & Amphibians
 - Fishes

Invertebrates
 - Mollusks
 - Echinoderms
 - Arthropods

 - Plants & Amber

 - Minerals
 - Meteorites
 - Geology