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Wildlife Wednesday: Sand Dollars (Arachnoides Tenuis)

Wildlife Wednesday: Sand Dollars (Arachnoides tenuis)

Have you ever picked up a white flat shell with a beautiful five petal flower pattern engraved into it on the beach? This in fact is the endoskeleton of a flat sea urchin, the sand dollar (Arachnoides tenuis). It belongs to the echinoidea class, making it related to the sea urchins, sea stars and sea cucumbers.

The top surface of the sand dollar has this five petal pattern created by the 5 sets of tubes. These tubes extend from the petals which the sand dollar uses for respiration. Its underside has spines that it uses to move along the sand bottom and to burrow into the sand to seek protection and food.

The sand dollar belongs to a story called the Legend of the Sand Dollar, which references Easter, Christmas and Jesus. Some references say that the 5-pointed “star” in the center of the top of the sand dollar’s shell is said to represent the Star of Bethlehem that guided the wise men to the baby Jesus. Also the underside, it is said that it’s the outline of a Christmas poinsettia. The most popular part of the legend is that the sand dollars are washed up mermaid coins or coins from Atlantis.

Sophia Dahl

Sand dollar petal pattern

Variation in sand dollars, in size and the 5 petal pattern (by Sophia Dahl).

Sand dollar underside

The underside of the larger sand dollar revealing where the spines once were located (by Sophia Dahl).

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