Sand dollars (also known as a sea cookie or snapper biscuit in New Zealand, or pansy shell in South Africa) are species of flat, burrowing sea urchins belonging to the orderClypeasteroida. Some species within the order, not quite as flat, are known as sea biscuits. Sand dollars can also be called "sand cakes" or "cake urchins".[2]
Sand dollars are small in size, averaging from three to four inches.[3] As with all members of the order Clypeasteroida, they possess a rigid skeleton called a test. The test consists of calcium carbonate plates arranged in a fivefold symmetric pattern.[4] The test of certain species of sand dollar have slits called lunules that can help the animal stay embedded in the sand to stop it from being swept away by an ocean wave.[5] 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 anus of sand dollars is located at the back rather than at the top as in most urchins, with many more bilateral features appearing in some species. These result from the adaptation of sand dollars, in the course of their evolution, from creatures that originally lived their lives on top of the seabed (epibenthos) to creatures that burrow beneath it (endobenthos).
The term "sand dollar" derives from the appearance of the tests (skeletons) of dead individuals after being washed ashore. The test lacks its velvet-like skin of spines and has often been bleached white by sunlight. To beachcombers of the past, this suggested a large, silver coin, such as the old Spanish dollar (diameter 38–40 mm). Sand dollars are named as such not for their monetary value, but because of their appearance.
Other names for the sand dollar include sand cakes, pansy shells, snapper biscuits, cake urchins, and sea cookies. [6] In South Africa, they are known as pansy shells from their suggestion of a five-petaled garden flower. The Caribbean sand dollar or inflated sea biscuit, Clypeaster rosaceus, is thicker in height than most. In Spanish-speaking areas of the Americas, the sand dollar is most often known as galleta de mar (sea cookie); the translated term is often encountered in English.
Behavior and habitat
A sand dollar digging into the sand on the Playa Novillero beach at low tide on the Pacific coast of Mexico
The spines on the somewhat flattened topside and underside of the animal allow it to burrow or creep through the sediment when looking for shelter or food. Fine, hair-like cilia cover these tiny spines.[7] Sand dollars usually eat algae and organic matter found along the ocean floor, though some species will tip on their side to catch organic matter floating in ocean currents.[5]
Sand dollars frequently gather on the ocean floor, in part to their preference for soft bottom areas, which are convenient for their reproduction.[why?] The sexes are separate and, as with most echinoids, gametes are released into the water column and go through external fertilization. The nektoniclarvae metamorphose through several stages before the skeleton or test begins to form, at which point they become benthic.
In 2008, biologists discovered that sand dollar larvae will clone themselves for a few different reasons. When a predator is near, certain species of sand dollar larvae will split themselves in half in a process they use to asexually clone themselves when sensing danger. The cloning process can take up to 24 hours and creates larvae that are 2/3 smaller than their original size which can help conceal them from the predator.[8] The larvae of these sand dollars clone themselves when they sense dissolved mucus from a predatory fish. The larvae exposed to this mucus from the predatory fish respond to the threat by cloning themselves. This process doubles their population and halves their size which allows them to better escape detection by the predatory fish but may make them more vulnerable to attacks from smaller predators like crustaceans. Sand dollars will also clone themselves during normal asexual reproduction. Larvae will undergo this process when food is plentiful or temperature conditions are optimal. Cloning may also occur to make use of the tissues that are normally lost during metamorphosis.
The flattened test of the sand dollar allows it to burrow into the sand and remain hidden from sight from potential predators.[5] Predators of the sand dollar are the fish species cod, flounder, sheepshead and haddock. These fish will prey on sand dollars even through their tough exterior.[7]
Sand dollars have spines on their bodies that help them to move around the ocean floor. When a sand dollar dies, it loses the spines and becomes smooth as the exoskeleton is then exposed.[9]
Evolution
The ancestors of sand dollars diverged from the other irregular echinoids, namely the cassiduloids, during the early Jurassic,[10] with the first true sand dollar genus, Togocyamus, arising during the Paleocene. Soon after Togocyamus, more modern-looking groups emerged during the Eocene.[1]
^"Sand Dollar Facts". ThoughtCo. Retrieved 2020-01-20.
^ abEncyclopedia of Animals. Great Neck Publishing. 2017.
^"Sand Dollar Printout - Enchanted Learning Software". Enchanted Learning. 2000.
^ abcGrzimek, Bernhard (2004) [2003]. Grzimek's animal life encyclopedia. Neil Schlager, Donna Olendorf, American Zoo and Aquarium Association (2nd ed.). Detroit: Gale. ISBN0-7876-5362-4. OCLC 49260053.
^"Everything You Need to Know About the Sand Dollar » Sand Dollar Shelling Marco Island Boat Tours". 29 November 2021.
^ abSayre, April Pulley (1996). Seashore (1st ed.). New York: Twenty-First Century Books. ISBN0-8050-4085-4. OCLC 34516888.
^Choi, Charles Q. (May 2008). "Split Defense". Scientific American. 298 (5): 38. Bibcode:2008SciAm.298e..38C. doi:10.1038/scientificamerican0508-38b – via Science Reference Center.
^"9 things you don't know about sand dollars". MNN - Mother Nature Network. Retrieved 2020-04-01.
Video showing the life cycle of Clypeaster subdepressus
January 31, 2023
sand, dollar, 2014, film, sand, dollars, film, also, known, cookie, snapper, biscuit, zealand, pansy, shell, south, africa, species, flat, burrowing, urchins, belonging, order, clypeasteroida, some, species, within, order, quite, flat, known, biscuits, also, c. For the 2014 film see Sand Dollars film Sand dollars also known as a sea cookie or snapper biscuit in New Zealand or pansy shell in South Africa are species of flat burrowing sea urchins belonging to the order Clypeasteroida Some species within the order not quite as flat are known as sea biscuits Sand dollars can also be called sand cakes or cake urchins 2 Sand dollarsTemporal range 56 0 Ma PreꞒ Ꞓ O S D C P T J K Pg N Late Paleocene to Recent 1 A live individual of Clypeaster reticulatus Mayotte Scientific classificationKingdom AnimaliaPhylum EchinodermataClass EchinoideaSuperorder GnathostomataOrder ClypeasteroidaSuborders and familiesSee text Contents 1 Anatomy 2 Suborders and families 3 Common name 4 Behavior and habitat 5 Evolution 6 Folklore 7 References 8 External linksAnatomy Edit Leodia sexiesperforata by Louis Agassiz 1841 Examples of Rotulidae Encope emarginata aboral and oral faces by Ernst Haeckel 1904 Clypeaster rosaceus aboral and oral faces by Ernst Haeckel 1904 Sand dollars are small in size averaging from three to four inches 3 As with all members of the order Clypeasteroida they possess a rigid skeleton called a test The test consists of calcium carbonate plates arranged in a fivefold symmetric pattern 4 The test of certain species of sand dollar have slits called lunules that can help the animal stay embedded in the sand to stop it from being swept away by an ocean wave 5 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 anus of sand dollars is located at the back rather than at the top as in most urchins with many more bilateral features appearing in some species These result from the adaptation of sand dollars in the course of their evolution from creatures that originally lived their lives on top of the seabed epibenthos to creatures that burrow beneath it endobenthos Echinocyamus pusillus alive Living sand dollar Eccentric sand dollars Dendraster excentricus at Monterey Bay Aquarium Echinarachnius parma family Echinarachniidae Mellita quinquiesperforata test Clypeasteridae Clypeaster reticulatus test Clypeasteridae Echinodiscus tenuissimus test Astriclypeidae Clypeaster aegypticus showing internal buttressesSuborders and families EditAccording to World Register of Marine Species sub order Clypeasterina family ClypeasteridaeL Agassiz 1835 family FossulasteridaePhilip amp Foster 1971 family ScutellinoididaeIrwin 1995 family Conoclypidaevon Zittel 1879 family FaujasiidaeLambert 1905 family OligopygidaeDuncan 1889 family PlesiolampadidaeLambert 1905 sub order Scutellina infra order Laganiformes family EchinocyamidaeLambert amp Thiery 1914 family FibulariidaeGray 1855 family LaganidaeDesor 1858 infra order Scutelliformes family EchinarachniidaeLambert in Lambert amp Thiery 1914 family EoscutellidaeDurham 1955 family ProtoscutellidaeDurham 1955 family RotulidaeGray 1855 super family ScutellideaGray 1825 family AbertellidaeDurham 1955 family AstriclypeidaeStefanini 1912 family DendrasteridaeLambert 1900 Pacific eccentric sand dollar family MellitidaeStefanini 1912 Keyhole sand dollars family MonophorasteridaeLahille 1896 family ScutasteridaeDurham 1955 family ScutellidaeGray 1825 family TaiwanasteridaeWang 1984 family ScutellinidaePomel 1888a Underside of live Mellita quinquiesperforata A number of sand dollars on the seabed Sand dollar beneath the sand at low tide on Hilton Head Island Live sea biscuit Clypeaster rosaceus commonly found off Key Biscayne FloridaCommon name EditThe term sand dollar derives from the appearance of the tests skeletons of dead individuals after being washed ashore The test lacks its velvet like skin of spines and has often been bleached white by sunlight To beachcombers of the past this suggested a large silver coin such as the old Spanish dollar diameter 38 40 mm Sand dollars are named as such not for their monetary value but because of their appearance Other names for the sand dollar include sand cakes pansy shells snapper biscuits cake urchins and sea cookies 6 In South Africa they are known as pansy shells from their suggestion of a five petaled garden flower The Caribbean sand dollar or inflated sea biscuit Clypeaster rosaceus is thicker in height than most In Spanish speaking areas of the Americas the sand dollar is most often known as galleta de mar sea cookie the translated term is often encountered in English Behavior and habitat Edit source source source source source source source source source source A sand dollar digging into the sand on the Playa Novillero beach at low tide on the Pacific coast of Mexico source source source source source source source source source source source source source source Spines on the underside of a sand dollar on the beach at Hilton Head Island South Carolina Sand dollars can be found in temperate and tropical zones along all continents 3 Sand dollars live in waters below the mean low water line on or just beneath the surface of sandy and muddy areas The common sand dollar Echinarachnius parma can be found in the Northern Hemisphere from the intertidal zone to the depths of the ocean while the keyhole sand dollars three species of the genus Mellita can be found on many a wide range of coasts in and around the Caribbean Sea The spines on the somewhat flattened topside and underside of the animal allow it to burrow or creep through the sediment when looking for shelter or food Fine hair like cilia cover these tiny spines 7 Sand dollars usually eat algae and organic matter found along the ocean floor though some species will tip on their side to catch organic matter floating in ocean currents 5 Sand dollars frequently gather on the ocean floor in part to their preference for soft bottom areas which are convenient for their reproduction why The sexes are separate and as with most echinoids gametes are released into the water column and go through external fertilization The nektonic larvae metamorphose through several stages before the skeleton or test begins to form at which point they become benthic In 2008 biologists discovered that sand dollar larvae will clone themselves for a few different reasons When a predator is near certain species of sand dollar larvae will split themselves in half in a process they use to asexually clone themselves when sensing danger The cloning process can take up to 24 hours and creates larvae that are 2 3 smaller than their original size which can help conceal them from the predator 8 The larvae of these sand dollars clone themselves when they sense dissolved mucus from a predatory fish The larvae exposed to this mucus from the predatory fish respond to the threat by cloning themselves This process doubles their population and halves their size which allows them to better escape detection by the predatory fish but may make them more vulnerable to attacks from smaller predators like crustaceans Sand dollars will also clone themselves during normal asexual reproduction Larvae will undergo this process when food is plentiful or temperature conditions are optimal Cloning may also occur to make use of the tissues that are normally lost during metamorphosis The flattened test of the sand dollar allows it to burrow into the sand and remain hidden from sight from potential predators 5 Predators of the sand dollar are the fish species cod flounder sheepshead and haddock These fish will prey on sand dollars even through their tough exterior 7 Sand dollars have spines on their bodies that help them to move around the ocean floor When a sand dollar dies it loses the spines and becomes smooth as the exoskeleton is then exposed 9 Evolution EditThe ancestors of sand dollars diverged from the other irregular echinoids namely the cassiduloids during the early Jurassic 10 with the first true sand dollar genus Togocyamus arising during the Paleocene Soon after Togocyamus more modern looking groups emerged during the Eocene 1 Folklore EditDead sand dollars are sometimes said to represent coins lost by mermaids or the people of Atlantis Some Christian missionaries found symbolism in the fivefold radial pattern and dove shaped internal structures comparing the holes with the crucifixion wounds of Christ and other features with the Star of Bethlehem an Easter lily a poinsettia and doves 11 References Edit a b The Paleobiology Database Sand Dollar Facts ThoughtCo Retrieved 2020 01 20 a b Encyclopedia of Animals Great Neck Publishing 2017 Sand Dollar Printout Enchanted Learning Software Enchanted Learning 2000 a b c Grzimek Bernhard 2004 2003 Grzimek s animal life encyclopedia Neil Schlager Donna Olendorf American Zoo and Aquarium Association 2nd ed Detroit Gale ISBN 0 7876 5362 4 OCLC 49260053 Everything You Need to Know About the Sand Dollar Sand Dollar Shelling Marco Island Boat Tours 29 November 2021 a b Sayre April Pulley 1996 Seashore 1st ed New York Twenty First Century Books ISBN 0 8050 4085 4 OCLC 34516888 Choi Charles Q May 2008 Split Defense Scientific American 298 5 38 Bibcode 2008SciAm 298e 38C doi 10 1038 scientificamerican0508 38b via Science Reference Center 9 things you don t know about sand dollars MNN Mother Nature Network Retrieved 2020 04 01 Rapid Evolution in Echinoids Archived 2011 07 27 at the Wayback Machine Lassalette Hilda December 1976 The Legend of the Sand Dollar churchofjesuschrist org Retrieved January 11 2019 External links Edit Wikimedia Commons has media related to Clypeasteroida Clypeasteroida Integrated Taxonomic Information System The Common Sand Dollar by Cheryl Page Video showing the life cycle of Clypeaster subdepressus Retrieved from https en wikipedia org w index php title Sand dollar amp oldid 1131471672, wikipedia, wiki, book, books, library,
