Echinoderms are all marine species, meaning they exclusively live in seawater. There are no freshwater or terrestrial echinoderms.
Echinoderm bodies are generally composed of calcium plates or shell-like structures that can be kept together tightly or loosely depending on the organism.
Echinoderms, which include starfish, sand dollars, and sea urchins, are members of the phylum Echinodermata.
All echinoderms have bumps (starfish), spikes (sea cucumbers), or spines on their bodies (sea urchins).
In the 19th and 20th centuries, they were the most often used species in regeneration research.