Echinoderms

Biology  Feeding   Reproduction   Site Species Summaries   Local Species   References

Welcome to the wonderful world of echinoderms! This page was created as part of Dr. Bonnie Becker's Marine

Ecology course at the University of Washington, Tacoma. Each student was required to select a phylum associated with

the inter tidal zones of the marine environment and become the "specialist" for that phylum. On this site, you will find

information about the phylum Echinodermata: what they are, where they live, and how they live. You will also find some

information about the more common echinoderms in the Puget Sound and Washington coast regions and lists of the

various kinds of life encountered by the author at the sites visited by the class.

       From the Greek words echin; meaning "spiny" and derma; meaning "skin", echinoderms belong to the phylum

Echinodermata and are sessile or slow moving invertebrates. There are over 7000 species and all are marine, with

the phylum being divided into six classes. Class Asteroidea are the Sea Stars that are sometimes called Starfish, but

are actually  not fish at all. They will generally have five arms (although some species have many more), radiating from a

central disk and are often found clinging to rocky substrates of one form or another (the image at the top of the page is

that of Henricia leviuscula, the Blood Star). Class Ophiuroidea are known as Brittle Stars, and while they may

superficially resemble sea stars, they have a much more pronounced central disk and their

arms are long and flexible.

The Daisy Brittle Star (Ophiopholis aculeata). Photo from Elasmodiver.com

Class Echinodea contains the very recognizable Sea Urchins and Sand Dollars. These

species have no arms, but do have a shell-like internal skeleton known as a test. Sand dollar tests are what the

beachcomber will often find washed up on the shore.

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The Pacific or Eccentric Sand Dollar, Dendraster eccentricus. Photo from Elasmodiver.com.

Class Holothuroidea are the Sea Cucumbers, and at first glance, they have little resemblance to

other echinoderms. They have no spines and their endoskeleton is greatly reduced, but they share certain traits with

other echinoderms that clearly show they do indeed belong in this phyla (See the section on Biology).

The California Sea Cucumber (Parastichopus californicus) Photo from Elasmodiver.com

The above four classes contain examples of species that can be found in the intertidal zones; the areas of beaches and

shorelines that become exposed when the tides are low, but there are two other classes of echinoderms that are

considered deep water species and are not likely to be seen by the average beachcomber or diver. Class Crinoidea

contains animals known as Sea Lilies and Feather Stars. Both are considered suspension feeders . The last class is

Concentricycloidea and contains rare deep water animals known as a Sea Daisies.

Echinoderms occupy a wide range of habitats from intertidal zones (some Sea Stars and Sea Cucumbers)

to deep water (Sea Daisies and Sea Lilies). Nearly all species are benthic, living on the bottom on one type of substrate

or another: rocks, sandy bottoms, mud, and even on docks and pilings. Some may live in sheltered areas, under rocks or

in tide pools and some live fully exposed to the surf and the currents.

This web site was created by Geoff King for Dr. Bonnie Becker's Marine Ecology class. May, 2008. It is part of the

UWT Marine Ecology 2008 Class Project. URL address: http://courses.washington.edu/mareco08