Sand Dollars

One of the most popular and sought after seashell is the sand dollar sea shell (echinarachnius parma). When they reach us at the beach, they are typically bleached white from the sun, round in shape and show no signs of ever having once been alive. So, what are sand dollars like when they're alive?

When alive, sand dollars are covered with many tiny, maroon colored, hairlike spines. These spines work a lot like the legs of a centipede or spider and allow the sand dollar to move around the ocean floor as well as pick up food. The flower petal-like pattern on the sand dollar’s shell is actually 5 paired rows of pores. These pores are holes in the endoskeleton through which the podia, used like fish gills, project from the body to allow the sand dollar to "breathe". Like the sea star, sand dollars have their mouths on their stomachs. The spines around their mouth gather and push small microorganisms into their mouth. Sand dollars live in the intertidal zone (the area between high tide and low tide) in the ocean.

Sand dollars have few natural enemies due to their hard, protective shells and the precious little edible parts to them. One of their few known enemies is the thick-lipped, eelpout (also known as an ocean pout or zoarces americanus).

The best time to find sand dollar seashells is right after a big storm. The waves will have dredged up many of the dead, discarded shells from the ocean floor. If you are not concerned with preserving the shell for your collection, I would suggest breaking it open. You may find many hard, white loose pieces inside. These were the sand dollars teeth!

Why are Seashells Different Colors?

Seashells are some of the most beautiful, mysterious and interesting products of ocean life (at least in my humble opinion). They have been incorporated into human societies for thousands of years as tools, art, jewelry, and money. Sometimes even as religious icons or symbols.

The colorful shells that we pick up in the sand on beaches are created by marine mollusks which are generally defined as soft-bodied invertebrates that create calcified shells for protection, camouflage and/or a place to live. Typically we're referring to snails, sea slugs and even squids and octopi (which do not have hard shells, but are still part of the mollusk family). The shells are composed mostly of CaCO3, or calcium carbonate, which is also found in rock, eggshells, and pearls and is the main cause of hard water. But, CaCO3 is white in color. The colors we see in seashells are often caused by impurities and waste from the organism captured in the shell when it is formed. Coloration is dictated mostly by diet and the water environment the creature lives in. For example, cowries that live and feed on coral, have shells that take on the same hues as the coral. This natural chemical reaction also helps to protect them from predators by allowing them to blend in with their environment.

What about all those iridescent shells that are multicolored and shiny? There's a different process that creates that effect. This iridescence is called mother-of-pearl and is caused by a coating of nacre on the shells. The nacre is secreted by oysters and some other mollusks to protect their bodies from parasites and disease. The nacre coating is very thin, in the range of several hundred nanometers thick, but is very strong and resilient. This nacre is also the same substance that composes pearls.