Sand Dollars

We've been having minus low tide mornings the past few days. Negative one foot plus and I feel like I'm walking on the sea floor taking a look at everything left for my discovery. As always, sand dollars are plentiful on our beaches and never cease to amaze seasoned walkers and tourists. 

The white sun bleached skeletons often end up as souvenirs in visitor's bags. I'm most intrigued by the live sand dollars, purple, cilia (little hairs) moving them through the sand. I imagine their slow struggle an effort to make it back to the water before the sun dries them out.

Check out this incredible high speed link to see a sand dollar moving 

Sand Dollar in Motion


Wikipedia provides this quick blurb on the anatomy of a sand dollar that might be of interest. It is easy to forget that this beautiful "shell" is or was a living creature and here's how it does it's thing:

The bodies of adult sand dollars, like those of other echinoids, display radial symmetry. The petal-like pattern in sand dollars consists of five paired rows ofpores. The pores are perforations in the endoskeleton through which podia for gas exchange project from the body. The mouth of the sand dollar is located on the bottom of its body at the center of the petal-like pattern. Unlike other urchins, the bodies of sand dollars also display secondary front-to-back bilateral symmetry. The anus of sand dollars is located at the back rather than at the top as in most urchins, with many more bilateral features appearing in some species. These result from the adaptation of sand dollars, in the course of their evolution, from creatures that originally lived their lives on top of the seabed (epibenthos) to creatures that burrow beneath it (hyperbenthos).