The Great Barrier Reef Library

A comprehensive guide to The Great Barrier Reef

Echinodermata – Starfish and Sea Cucumbers


By on December 26, 2017


Echinodermata are bottom-dwelling, marine invertebrates and The Great Barrier Reef is home to 630 different species.1 They can be found all over the world from shallow sea-shores, right down to the abyssal depths. Echinoderms exhibit pentamerous radial symmetry. This means that you can divide them into five similar portions around the central axis.

Calcareous plates make up The Echinoderm skeleton, although they vary in form between each group. They fuse together in Sea Urchins, fit loosely together in Sea Stars and Sea Cucumbers have them reduced to small spicules in the skin. Calcite makes up the Echinoderm skeletal plates. This differs from most marine skeletons in that it has an extra Magnesium Carbonate molecule.

The other unique feature of Echinodermata, are their little tube feet (Podia). The Podia are primarily responsible for movement, but may also be used for respiration and burrowing. A water vascular system connects the podia, which branches out further to each arm or body segment, allowing for movement. The stone canal is a simple tube that is responsible for maintaining the system and keeping it topped up with fluid. The stone canal connects to the ring canal, which further connects to a structure called The Madreporite. The Madreporite is a sieve-like external opening that allows water to enter. Unfortunately, it also makes Echinoderms particularly susceptible to pollution, as water enters directly into the body cavity.2,3

You can find a list of all of the groups of Echinodermata found in The Great Barrier Reef Marine Park, below.

Class – Next level of classification, grouping animals with similar characteristics