Sand Dollar
by Pam Holdsworth
Title
Sand Dollar
Artist
Pam Holdsworth
Medium
Photograph - Photography
Description
Sand dollars, like all members of the order Clypeasteroida, possess a rigid skeleton known as a test. The test consists of calcium carbonate plates arranged in a fivefold radial pattern.[2] In living individuals, the test is covered by a skin of velvet-textured spines which are covered with very small hairs (cilia). Coordinated movements of the spines enable sand dollars to move across the seabed. The velvety spines of live sand dollars appear in a variety of colors�green, blue, violet, or purple�depending on the species. Individuals which are very recently dead or dying (moribund) are sometimes found on beaches with much of the external morphology still intact. Dead individuals are commonly found with their empty test devoid of all surface material and bleached white by sunlight.
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 of pores. 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 ass of sand dollars is located at the back rather than at the top as in most urchins, with many more bioligical features appearing in all species. These result from the adaptation of sand dollars, in the course of their evolution, from creatures that originally lived their lives below the seabed (epibenthos) to creatures that burrow beneath it (endobenthos).
Using my photo of the sand dollar and textures from Jai Johnson's 'Daily Texture' and Topaz Impressionists,I was able to create this beautiful painterly image.
The common sand dollar, Echinarachnius parma, is widespread from intertidal zones to considerable depths in the ocean waters of the Northern Hemisphere. It can be found in temperate and tropical zones. The keyhole sand dollar (three species, genus Mellita) is found on a wide range of coasts in and around the Caribbean Sea.
Uploaded
May 30th, 2016
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