Today I will be talking about Sand Dollars (this specific species is a Florida Keyhole, alive on the left and dead on the right)! Other names they are known by is sea cookie, sea biscuit, snapper biscuit, and pansy shell. They are under the Phylum Echinodermata along with sea urchins, sea stars, and sea cucumbers. Spines covered in cilia cover their bodies and serve different purposes in difference areas. Along the bottom of their bodies they help them move and burry their bodies in the sandy sea floor they call home. They can carry food such as algae, plankton, crustacean larvae and small copepods to their mouth (“Aristotles Lantern”) in the center. The mouth can break into 5 even pieces called “white doves.” The long opening below their mouth is their anus. The 5 petelloids have specialized feet-like structures called “podia” they use for gas exchange in the water. The other openings are called “lunules” which can vary in amount and arrangement for each species. They serve a dual purpose of allowing water to pass through so they don’t get picked up in areas of high water flow and if food enters through the top, they can move it to their mouths. Their white calcium carbonate bodies (“tests”) are covered by soft leathery spines, which is one of the ways to distinguish a live one from a dead one. If you pick one up, hold it gently and don’t move, you’ll feel their spines moving on your hand. They can only survive out of the water for a few minutes, so make sure to place them back gently on the sand with their bottom side down! Calcium carbonate forms by a Ca ion bonding with carbonic acid (H2CO3). If there is too much carbonic acid and not enough dissolved Ca, then the calcium carbonate they need to build their “tests” is not as abundant for use, resulting in them being more fragile.
Originally posted on 3 March 2020
(not my pictures)
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