Size of the fossilized sea urchin about 7 - 9cm
Origin: Madagascar
Phylum: Echinoderms (Echinodermata)
Class: Sea urchins (Echinoidea)
Order: Sand dollars
In contrast to "real" sea urchins, the sand dollars belonging to the irregular sea urchins (Irregularia) have no spines. However, they fascinate the observer and collector by their perfect fivefold division. The animals are very flat and have a skeleton composed of small calcareous plates covered by thin tissue and many cilia. With the help of these small hairs, which are constantly in motion, the plankton in the sea is waved over the body to the mouth opening of the sand dollar. In the mouth opening sits a five-pointed structure covered with regrowing teeth, the so-called "lantern of Aristotle". The individual elements of this jaw apparatus can be moved against each other and thus rasp the food of the sand dollar into small pieces. Since the Greek scholar Aristotle (384 B.C. to 322 B.C.) was the first to describe this anatomical peculiarity of these fossils, they now bear his name in his honor.
Like many other echinoderms, sand dollars can slowly move forward with the help of their ambulacral system. This system consists of several channels inside the animals that are filled with a fluid. The channels end in small tentacle-like feet. These little feet extend forward in the desired direction of movement, then attach themselves to the substrate, and then shorten again. This shortening then causes the entire body of the animal to follow suit.
The name "sand dollar" is derived from the flat shape and color of the animals, which resembles a coin. In some Spanish-speaking countries, sand dollar fossils are also called "galleta de mar", meaning "sea cookie".