echinoderm – invertebrate marine animals with spiny skin including starfish, sea urchins and sea cucumbers

(Pronounced eh-kai-nuh-derm)

To remember the meaning of echinoderm, associate it with starfish and use the following mnemonic:

The elephant shaped kite was pierced by a number of hypodermic (echinoderm) needles, and no longer flew, much to the starfish's disappointment. 

Echinoderms are a distinct phylum (see taxonomy) of exclusively marine animals characterised by their spiny or bumpy skin (echinoderm literally means 'spiny skin') made of calcium carbonate and embedded into their skin. Although they are invertebrates, these thousands of calcium carbonate components do form a unique type of skeleton. Another feature is their water vascular system, a network of water-filled canals what connect to hundreds of small, hollow tube feet which can extend and contract to allow the animal to move, grip surfaces and capture food.

The phylum includes five marine classes, these are: starfish, that are predators, capable of remarkable regeneration (ability to grow back severed body parts), brittle stars with flexible arms, sea urchins with spherical bodies, sea cucumbers with elongated soft bodies, and sea lilies that are filter feeders. 

Echinoderms play crucial ecological roles in marine ecosystems as both predators and prey.