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Phylum Echinodermata

Sea Stars, Brittle Stars, Sea Cucumbers, Sea Urchins, Sand Dollars, and Feather Stars

Books About Echinoderms

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The Ochre Sea Star (Piaster ochraceus), an echinoderm of Class Asteroidea, displaying the beautiful varieties of color typical for this species.  On close inspection of the photo on the right the madreporite, a small round hole in the center of the animal can be seen.  This structure is actually the anus of the Sea Star and undigested food exist the animal from here; the mouth is found in the center of the the bottom (oral) surface.  A magnifying glass or microscope would reveal tiny organs called pedicellaria on the upper (aboral) surface of the sea star.  These organs are miniature pincers that attack and remove parasites or other small organisms that land on the star.

Refrigerated Mini-Ocean Aquarium - Self-Contained Unit Ensures Your Marine Life Will Thrive.

Nice series of photos that demonstrate the interesting skin of the echinoderms.  This Ochre Sea Star in the above photo displays the "spiny skin" from which the phylum draws its name.  The yellow spot in the above left picture is the anal opening, and the upper left photo shows the sea star "eye," a light sensitive organ.  Flipping our sea star over the bottom pictures highlight the tube feet of the animal used for locomotion and attachment to prey.  Note that this Ochre Sea Star (an unusually large specimen, over one foot in diameter) has only four feet instead of the typical four. 

Basic Full Size Biological Microscope - An excellent student-quality student microscope.

Phylum Echinodermata:

Class Crinoidea - Sea Lillies and Feather Stars

Class Asteroidea - Sea Stars (Star Fish)

Class Ophiuroidea - Brittle Stars and Basket Stars

Class Echinoidea - Sea Urchins and Sand Dollars

Class Holothuroidea - Sea Cucumbers

Some not so cozy invertebrates that still manage to be loved by everyone are the Echinoderms.  Some of our most familiar and extraordinary sea shore wildlife make up this phylum of interesting creatures.  Over 5300 different echinoderms are known worldwide and the Northwest is blessed by 180 species of this particular wildlife.  Colorful, accessible, and generally harmless our shores team with all manner of Sea Stars, Brittle Stars, and Feather Stars.  So many Sand Dollars lie just beneath the surface on sandy beaches that the shore feels lumpy under under your feet.  Plunge your hands into the sand and you'll easily bring up 10 or 20.  Sea Urchins are always a familiar, instantly recognizable sight.  Sea Cucumbers, a little less familiar than their spiny cousins, abound nonetheless.

A nice plump Sunflower Star (Pycnopodia helianthoides) is pictured on the left.  Only too familiar to crab fisherman, the Sunflower Star is the largest (up to 18 inches) and fastest moving star in the Pacific Northwest.  (Note the Red Rock crab to the right of the Sunflower star.)  To the right is the beautifully colored Vermillion Star (Mediaster aequalis), also called the Red Sea Star or Equal Sea Star for its pleasing symmetry.

On the left is a Leather Star, Dermasterias imbricata.  Up to 8 inches in radius Leather Stars are reputed to smell like garlic or sulfur, a claim I cannot confirm.  The photo was taken at the Seattle Aquarium and does not do justice to the animal which normally displays red or orange spots.  I took the photo of the oddly named Fat Henrica, Henrica sanguinolenta, in Puget Sound at a depth of about 10 feet.  The picture is enhanced a bit, but the water was pretty murky when I snapped the picture.  You'll notice their distinct white color as you look into the depths from the side of a boat. 

Books About Echinoderms

    Although it may not looks like it, all echinoderms possess an internal skeleton.  Unlike our bony skeletons, the echinoderm model is composed of calcareous ossicles, another way of saying tiny bones composed of calcium carbonate.  A distinctive feature of this type of skeleton are projections that lend echinoderms their spiny appearance and their name which means "spiny skin."

    The echinoderms of Class Asteroidea contain the most familiar animals of this group.  Commonly lumped together under the nickname Sea Stars or Starfish, the Asteroidea are a diverse class of animal all built around a symmetrical, star shaped body.  Arms (or tentacles) project from the center and terminate in an "eye spot" just beneath the tentacle that is noticeably sensitive to light.     

    All Asteroidea are carnivores.  Most will feed on any kind of invertebrate or freely scavenge on dead animals, but some, like the Pacific Sun Star, are specialized for Sea Cucumbers.  I can testify to the fact, however, that they love chicken just as much.  

    This group of animals moves thanks to a remarkable arrangement of tube feet which are plainly visible on the ventral side of the animal.  Thousands of these little tube feet, in an amazing display of nervous system coordination, use hydraulic pressure and suction in order to transport the animal.  Just ot give you a idea of the variety of Northwest wildlife I've included a partial list of the Asteroidea in our region.  Also included are Brittle Stars and Basket Stars (Class Ophiuroidea): 

Sea Cucumbers come in many shapes and sizes.  On the left is the slug shaped California Sea Cucumber (Paratichopus californicus).  Nearly two feet long, the California Sea Cucumber is our largest.  To the right is a hydra shaped Orange Sea Cucumber (Cucumaria minata).

Class Holothuroidea, the Sea Cucumbers number about 5,000 species worldwide.  Distinguished from the rest of the echinoderms by an elongated "cucumber" shape and an internal skeleton much smaller than their cousins.  Sea cucumbers are normally drab in color, but some, like our own California Sea Cucumber (pictured below) exhibit rich, vibrant colors.  While most do not exceed a foot in length one species in the Philippines, stretches out to more than a yard long. 

    Our Northwest Sea Cucumbers display a range of morphology and color.  Most have the hydra shape body type of the Orange Sea Cucumber, but several, such as the California Sea Cucumber pictured above possess the classic cucumber shape. 

    The last echinoderm that we will consider are the Echinoidea, the Sea Urchins and Sand Dollars.  Echinoidea means "like a hedgehog" and you have to admit it would be harder to find a more apt description for a sea urchin.  A multi colored bunch sea urchins typically have a circular or oval shape surrounded by a projection of long spines.  These spines are not to be trifled with.  They can, and often do, inflict a painful wound.  Man and urchin often intersect at the foot of a human who has stepped on the urchin.  At the tip of each spin is a poison sac filled with a toxic substance.

The Eccentric Sand Dollar, Dendraster excentricus, just about actual size.  Their dried out skeletons often seen in souvenir shops, show no sign of the living beauty of the animal.  Purplish in color and covered with tiny hair like spines top and bottom they live by the millions just under the surface.  Sand dollars prefer sandy beaches where the little projections on their ventral surface (bottom right) filter food particles toward the mouth in the center.  The dorsal surface (bottom left) is a blanket of tiny spines that clean the animal.

    Although the spines are moveable and provide the urchin with transportation it does make you wonder how any animal with such a design manages to eat.  Simple.  Sea urchins feed on algae, kelp, and animal remains.  Turn over a sea urchin and you will see, in an are devoid or spines, a prominent pyramid shaped organ called Aristotle's Lantern.  Looking just like a beak composed of five calcareous plates this chewing organ can be partially projected from the body of the urchin.

    Sand Dollars are also urchins, but in this group of animals the body structure is flattened and the spines are severely reduced.  Evident in nearly every sea side gift shop throughout the world, they are a deep rich purple color when alive.  Like the sea stars sand dollars have thousands of tube feet that provide locomotion.  Turn a sand dollar over and you will see an incredible number of these feet for such a small creature.

Books About Echinoderms

 Protozoans  Sponges  Cnidarians  Ctenophores Arthropods  Echinoderms  Mollusks  Nematodes  Flatworms  Annelid Worms

Birds  Mammals  Reptiles  Amphibians  Fish  Invertebrates  Library  NWWOL Online Store Home

Mission  Editor Bio  Site Map   Contact   Wildlife Park Links  Further Study  Wild Employment  Northwest Trek