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Echinoderms - Phylum Echinodermata


Perfect Purple! starfish
Kerstin Meyer/Moment Open/Getty Images Green Sea Urchin

Green Sea Urchin (Strongylocentrotus drobachiensis). This image shows the urchin's spines and it's tube feet, which it uses for locomotion.

Blue Ocean Society Northern sea star

Northern Sea Star (Asterias vulgaris)

Blue Ocean Society


Echinoderms, or members of the Phylum Echinodermata, are some of the most easily-recognized marine invertebrates, many of which are found in tide pools or in the touch tank at your local aquarium.

The Phylum Echinodermata contains 5 classes: Asteroidea (sea stars), Ophiuroidea (brittle stars and basket stars), Echinoidea (sea urchins and sand dollars), Holothuroidea (sea cucumbers) and Crinoidea (sea lilies and feather stars.) They are a diverse group of organisms, containing about 6,000 species.


What Is An Echinoderm?:

Echinoderms have a unique body design. Many echinoderms have radial symmetry, which means that its components are arranged around a central axis in a symmetrical manner (so, an echinoderm has no "left" and "right" half, only a top side, and a bottom side.) This body plan is not as obvious in all echinoderms as it is in the sea star, which has several arms (often 5) arranged around a central disk.



Echinoderms also generally have spines, which are pronounced in sea urchins, but not as obvious in some of the other echinoderms.


Echinoderm Water Vascular System:


Instead of blood, echinoderms have a water vascular system, which is used for movement and predation. The echinoderm pumps sea water into its body through a sieve plate or madreporite, and this water fills the echinoderm's tube feet. The echinoderm moves by filling its tube feet with water to extend them, and using muscles within the tube feet to retract them. The tube feet also allows echinoderms to hold on to rocks, other substrates and prey by suction.


Echinoderm Reproduction:


Most echinoderms reproduce sexually. Echinoderms can be male and female, but they are indistinguishable from each other.They reproduce by releasing eggs or sperm into the water, which are fertilized and results in free-swimming larvae that later settle to the bottom.

Echinoderms can also reproduce asexually by regenerating body parts such as arms and spines.




Martinez, Andrew J. 2003. Marine Life of the North Atlantic. Aquaquest: New York.

Zubi, Teresa. 2009. "Invertebrates". Starfish. Accessed May 17, 2009.

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