Re: What are the doves inside Sand Dollars(once the test has been broken open)?

Hi Lauren,

When I first read your question, my immediate thought was, "Oh, the five doves must be part of Aristotle's lantern!" Then I did a little research, and it turns out I was right. Let me explain. First of all, what is Aristotle's lantern? It's the feeding structure of the echinoid echinoderms, a group that includes sea urchins as well as the sand dollars of your question. Sea urchins (for example, Strongylocentrotus) graze on algae and algal films, and their Aristotle's lantern is very muscular and well developed. It contains five structures called pyramids, arranged radially to form a sort of five-sided tent. Each pyramid has a long central band that extends from the base of the pyramid to the top of the pyramid, and a little bit beyond. This tip is called a tooth. Because there are five pyramids, the lantern has five teeth. There are lots of other structures associated with the lantern, but I won't trouble you with their names. If you watch an urchin in an aquarium, you might be able to see the teeth of the lantern when the urchin grazes on the glass. Here's a link to a photo of Aristotle's lantern in a dissected urchin: http:/ /virtual.yosemite.cc.ca.us/randerson/Marine%20Invertebrates/aristotl.htm

Sand dollars, on the other hand, are not grazers. Instead, they feed on particles that their tube feet collect from the oral surface of the animal. Since they don't graze on algae, and the particles they eat are very small, their Aristotle's lantern is much reduced compared to that of a sea urchin. To answer your question, here's what I found at a site describing the test of a sand dollar (http://www.science.lande r.edu/rsfox/mellita.html): "Examine one of the five jaws of Aristotle's lantern. The lantern of clypeasteroids is much simpler than that of the regular urchins and essentially consists of the five pyramids (see discussion under Strongylocentrotus) and their five teeth. The compasses, rotulae, and epiphyses are absent or vestigial. The five bird-shaped ossicles (sometimes called "doves" by the beachcombing public) are the pyramids of the lantern. The teeth are usually lost in dried preparations."
So there you have it. The "doves" that you found are the pyramids of the lantern.

Oh, and if you're interested in why this feeding structure is called Aristotle's lantern in the first place, this site has a good explanation: http ://lsvl.la.asu.edu/askabiologist/research/urchins/aristotle.html

Good luck with your project! I hope you enjoy studying these fascinating animals!

Allison J. Gong
Mad Scientist

Reference: Ruppert and Barnes, 1994. Invertebrate Zoology. Saunders College Publishing.