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Posts Tagged ‘echinoderm’

Sea Urchins: Spiny Shelled Sea Spheres

Posted by Greg on December 7, 2011

Purple Sea Urchin. Photo by Janek Pfeifer (Wikimedia Commons)

Just try to say that three times fast!

While I was doing the article on sea stars, my sources referenced sea urchins and sand dollars as related animals (echinoderm). Since I have sand dollar and sea star articles, it follows I should complete the set.  As with the first two, urchins are varied and beautiful in shape and color. According to the Tree of Life web project,  “sea urchins are sea creatures that live in oceans all over the world.  Similar to sea stars, sea urchins have a water vascular system. Their spherical shape is typically small, ranging from about 3 cm to 10 cm in diameter, and their bodies are covered with a spiny shell. The skeleton of a sea urchin is also known as the test. The shells within the test of these creatures are made up of packed, fitted plates which protect them from being damaged.  As for the spines outlining their shell, these are movable and help the sea urchin to camouflage or protect itself from predators. Sea urchins can vary greatly in colour.  Some of the most frequently seen colours are black, red, brown, purple and light pink.  On the bottom side of a sea urchin there are five teeth that these organisms use to ingest algae and break down other foods they consume to survive. These five teeth continually grow throughout the sea urchin’s life.  On the outside of their body, they also have hundreds of transparent tubes that emerge which allow them to stick to the bottom of the ocean or to move at a very slow pace.  These unusual tubes are called ‘tube feet.’  Their tube feet are much longer than the spines outlining their shells and they are also used by the sea urchin to trap food and in respiration.”

Two Urchins in a Coral Reef off the Coast of Kona, Hawaii. Photo by Mila Zinkova (Wikimedia Commons)

Sea urchins are found worldwide in both warm and cold ocean environments.  E.G.D. tells me she often saw them clinging to coral reefs and to crevices in rocks when she went snorkeling off the coast of Oahu. The Tree of Life web project article referenced above mentions that they also live in rock pools, kelp forests and sea grass beds and that they like to “lodge themselves half way into the surface of sand, mud or holes.”  They are able to access food in these areas since they feed on algae, sea grass and seaweed.

While admiring these creatures in tide pools and rock pools, please always follow tide pool etiquette.  Also, here’s a note from E.G.D.: if you’re snorkeling in Hawaii, please be careful not to step on the sea urchins!  They’re all over the place, and they aren’t always obvious to the eye.

Posted in Beach and Coastal Wildlife, Tide Pools | Tagged: , , , | Leave a Comment »

Starfish or Sea Star?

Posted by Greg on November 30, 2011

"Red-knobed Starfish" Photo by Adrian Pingstone (Wikimedia Commons)

Starfish, as sea stars were previously known, come in more varieties than I once thought. For one, they sometimes have more or fewer legs than the five we typically think of, and for another, there are thousands of species of this beautiful sea creature.

According to National Geographic, “marine scientists have undertaken the difficult task of replacing the beloved starfish’s common name with sea star because, well, the starfish is not a fish. It’s an echinoderm, closely related to sea urchins and sand dollars. There are some 2,000 species of sea star living in all the world’s oceans, from tropical habitats to the cold seafloor. The five-arm varieties are the most common, hence their name, but species with 10, 20, and even 40 arms exist.”  Some species have only four arms.

Giant sea star (sand star). Photo by NOAA (Wikimedia Commons)

Eleven Armed sea star. Photo by de.Benutzer:Hase (Wikimedia Commons)

Sea Stars come in many different, often brilliant colors. They use color to camouflage themselves for protection or to scare off potential predators. Another interesting fact from National Geographic is that “beyond their distinctive shape, sea stars are famous for their ability to regenerate limbs, and in some cases, entire bodies. They accomplish this by housing most or all of their vital organs in their arms. Some require the central body to be intact to regenerate, but a few species can grow an entirely new sea star just from a portion of a severed limb.”

Sea Stars are frequently found in tide pools. Please follow “Tide Pool Etiquette” while studying them in their element. *You might also be interested in our post on Morro Bay tidepooling*

Happy Sea Star searching!

Posted in Beach and Coastal Wildlife, Tide Pools | Tagged: , , , , , , | 3 Comments »

Cha ching! Sand Dollars. Fun to find.

Posted by Greg on November 23, 2011

Walking on a beach and finding sand dollars is a beachcomber’s delight. They often can be found on beaches where there is not much else to collect.

According to Cheryl Page at the Gulf of Maine Aquarium, sand dollars are from the class of marine animals known as Echinoids, spiny skinned creatures. Their relations include the sea lily, the sea cucumber, the star fish and the sea urchin. When alive, the local species, Echinarachnius parma is outfitted in a maroon-colored suit of moveable spines that encompass the entire shell. Like its close relative the sea urchin, the sand dollar has five sets of pores arranged petal pattern. The pores are used to move sea water into its internal water-vascular system which allows for movement. “

Sand dollars from Pismo Beach, California (©JodyDiehl)

There are several legends about the sand dollar. One version goes like this: There are five dove shapes locked inside the sand dollar. They hold a hidden promise. After a sand dollar dies and is broken open, the doves are released and come to life, ready to take flight and experience their freedom.

Live sand dollar (Photo from

Many of us have not seen a living sand dollar. We might think of them as bleach white because that’s what washes up on shore after they die. When they’re alive, they are actually very colorful. Some are green, some are black-purple and some are brown. If you have yet to see a living sand dollar, it is probably because they prefer to dwell under the sand. If you go snorkeling or scuba diving and run across a cache of the white, expired sand dollars, chances are that live ones are in the sand right underneath them, so please do not disturb.

You’ll want to make sure that the sand dollars you collect are not alive. There are fines involved in many beach areas for collecting live shells, and in many places sand dollars are included. According to Karie Partington of  Naples (Naples, Florida), “The live ones are tan in color and have a fine hairlike coating. They also secrete a yellowish, iodine-based substance that gets on your hands if you pick them up. The dead ones are white and hairless. In addition to the legality issue, there are other reasons to steer clear of collecting live sand dollars, said Jose Leal, director of the Bailey-Matthews Shell Museum on Sanibel Island. ‘Sooner or later the live ones are going to ooze and get slimy and smelly if you take them,’ he said.”(We’ll assume then that live sand dollars in the Naples, Florida area are tan in color.) The live sand dollar pictured in my hand (below) on a Southern California beach was purple and did not secrete anything on me.

Live Sand Dollar – Underside (©Jody Diehl)

Happy beachcombing!

More reading: Beachcombing? Shelling Regulations Abound. Know Before You Go!

Yummy and festive: How to make your own sand dollar cookies!


Posted in Beach and Coastal Wildlife, Beach Treasures - Beachcombing | Tagged: , , , , , , , | 17 Comments »

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