Wednesday, August 17, 2011

Eccentric Sand Dollar (Dendraster Excentricus)

the sun-bleached test of a dead eccentric sand dollar lying on the beach


When we visited the beach at Burfoot Park in Olympia last month, we noticed a lot of eccentric sand dollars lying on the wet sand.  The eccentric, or Pacific or Western, sand dollars are the only type of sand dollar in Oregon and Washington, and they are only found on the northeastern shores of the Pacific Ocean. They are called "eccentric" because of the off-center star or flower pattern which is positioned toward the back of the animal, and because the off-center position, it can stand itself up by burying its front end partly in the sand and feed on small organisms and other organic matter that pass by in the current (you can learn more about that at The West Coat's Living Sand Dollars). This type of sand dollar can grow up to four inches in size and can live 10-13 years.

We visited the beach when the tide was out (but coming in!), and sadly, we saw many dead sand dollars on the beach, and in one area the sun-bleached tests ("tests" are what their skeletons are called) of dead sand dollars covered much of the ground.  Some, though, were alive.

Sand dollars that are alive are pale gray-lavender to dark purplish black in color, and they are covered with thousands of velvet-textured spines. Those that are dead are light in color and smooth, lacking the velvety spines. This next picture shows a dead one on the left and a live one on the right.


If you, very gently, pick up a sand dollar and turn it over, you can see its spines and tube feet moving.

My older daughter carefully looking at the bottom an eccentric sand dollar.
The velvety spines of the eccentric sand dollar are purple.

My younger daughter is examining a sand dollar in the picture below. . .
Here are pictures she took of a sand dollar. . .
the top (or aboral side) of a live sand dollar

the bottom (or oral side) of a sand dollar

I took this picture of her holding a sand dollar. . .

another picture of the bottom side of a sand dollar


Here my daughter is standing in a "graveyard" of sand dollars. . .
the tests of dead sand dollars


There is one that is alive in the middle of so many that aren't living. . .
the purple one is a live sand dollar

I still have so much to learn about sand dollars.  Researching them has brought up more questions, so I think I might check out a book to learn more!  Here are some helpful online resources about sand dollars:

The West Coat's Living Sand Dollars
The Biogeography of the Western Sand Dollar (Dendraster Excentricus)
Eccentric sand dollar (South Sound marine life)
Sand Dollars on Tybee…Take the Test! -- This focuses on a different type of sand dollar, but has good information about how to "test" to see if a sand dollar is alive. 
Dendraster excentricus on wallawalla.edu
Sand Dollar on EnchantedLearning.com 
Sand Dollar on howstuffworks.com 
Introduction to the Echinoidea

~* This post is my entry for ABC Wednesday for the letter "E." *~ 
I'm also linking this to Watery Wednesday.

4 comments:

  1. an eclectic collection
    ROG< ABC Wednesday team

    ReplyDelete
  2. These look like interesting creatures. I'd vaguely heard of a sand dollar before, but had no idea what they were - or they were unique to only your part of the world. Exceptional.

    ReplyDelete
  3. Eu nunca ouvi falar desses seres vivos. Depois de ler sua postagem, fiz uma pesquisa para saber mais sobre eles. Muito obrigada por me informar sobre mais essa maravilha da natureza. Um post muito interessante e de fotos bonitas, como a quarta foto. Abraços a toda família aventureira.

    ReplyDelete
  4. Wow!! What a great post! I have several sand dollars, from the Atlantic coast of Canada, but have never stopped to learn about them. When you say there are a lot of tests, you mean it!! The first photo is my favourite, though!!

    ReplyDelete