The echinoderms - meaning spiny skin - are the starfish, sea urchins and sea cucumbers.
Starfish like the Bloody henry starfish and the Common starfish which live in our waters are predators that move across the seabed using special organs called tube feet.
Visible spines on the outside of urchins and on the skin of starfish and sea cucumbers are there to deter predators.
On the sandflats at St Martin’s and Tresco there are important populations of burrowing Heart urchins. Crevice Sea cucumbers and featherstars are often seen on reefs by divers.