Biology 11



Echinoderms for Dummies By Claudia CristescuPhylum Echinodermata is member of the kingdom Animalia and subkingdom Eumetazoa. They are commonly known to have radial symmetry and are mostly marine.Marine animal members of the Phylum Echinodermata include sea star, sea urchin, feather star and sea cucumber. Sea stars belong to the class Asteroidea, order Forcipulatida, family Asterinidae, genus Asterias and species Rosy Starfish.Sea urchins belong to the class Echinoidea, order Clypeasteroida, family Echinarachniidae, genus Echinarachnius, and species Sand dollar. Feather stars belong to class Crinoidea, order Comatulida, family Antedonidae, genus Antedon, and species Antedon bifida.Sea cucumbers belong to class Holothuroidea, order Aspidochirota, family Stichopodidae, genus parastichopus, species P. parvimensis. Sea UrchinsSea urchins have a five-sided radially symmetrical body, also known as pentamerism, and an external chitinous skeleton. Sea urchins have movable spines of various sizes and forms that are attached to the body and have a pincer-like pedicellaria for grabbing small prey. Appendages of sea urchins include multiple paired rows of tiny tube feet used in respiration and movement. Sea Urchin’s Nervous SystemThe center of the sear urchin is a large nerve ring from which five nerves radiate underneath the radial canals of the water vascular system and branch into even finer nerves to innervate the tube feet, spines, and the pedicellariae. A sea urchin’s body works as one compound eye, as it is sensitive to touch, light, and chemicals, even though it has no eyesight. Sea urchins have light-sensitive molecules, mostly in their tube feet and in tiny stalked appendages found in among their spines. Each spine can have about 140 light-sensitive cells. They have a diffused and small nerve net as the animals are more or less made of rock which makes it hard to examine their nervous system. Sea Urchin’s Digestive SystemSea urchin’s digestive system consists of tube joining a mouth at the bottom to an anus at the top. The mouth consists of a complex arrangement of muscles and plates surrounding the circular opening. Sea urchins have a centrally located jaw (called Aristotle's lantern) with horny teeth. Aristotle's lantern is made up of five hard plates that come together like a beak. The food is grasped and then it is passed up through a complexly coiled gut and the waste is passed upward through the anus. Sea urchins are mostly known to eat brown and green algae and decayed matter. Sea Urchin’s Respiratory SystemSea urchins have hundreds of transparent tubes that emerge which allow them to stick to the bottom of the ocean. These tubes are called “tube feet” and are much longer than the spines outlining their shells and they are also used by the sea urchin in respiration. A sea urchin breathes through its tube feet, where gases are exchanged, instead of in gills or lungs. “Aristotle's lantern," surround a sea urchin's mouth on the bottom of its shell. Sea Urchin’s MovementA sea urchin uses its many tube feet to hang on to the bottom of the ocean, move along rocks, sand or other surfaces. The tube feet of the sea urchins allow them to move by way of water vascular system and hydraulic pressure allowing it to extend or contract its feet. They can move fast, walking on their feet, their spines, or even their teeth. Hydraulic powered tube feet are unique to sea urchins and other echinoderms, which includes starfish, sea cucumbers, sea lilies and brittle stars. Sea Urchin’s Reproductive SystemSea-urchin species have separate sexes and release their gametes into the sea, mostly during the spring. The gonads are the reproductive organs for both males and females. The female sea urchin releases millions of tiny, jelly-coated eggs into the water that are then fertilized by the sperm of the male sea urchin. Metamorphosis is usually complete within a week. The tiny sea urchin eggs become part of the plankton and the sea urchin babies (larvae) do not hatch for several months. The sea urchin young will not become large enough to retreat from the plankton and down to the ocean floor until they are between 2 and 5 years old. Fun FactsSea urchins can eat almost anything and their sharp teeth can scrape algae off rocks, and grind up plankton, kelp, periwinkles, and sometimes even barnacles and mussels.Sea urchin behavior can signal poor water quality, as they show stress in polluted water.When sea stars get close to a sea urchin, the urchin moves its spines aside and lets the sea star's arm get really close until the pincers chomp on the sea star's tube feet.When a sea urchin dies, all its spines fall off, leaving only the spherical test.The sea urchin gets its name from an old English word for the spiny hedgehog which is similar to the American porcupine. Reference (image)Antedon bifida, Com. (n.d.). Retrieved May 17, 2016, from . (2011, November 23). Beach Treasures and Treasure Beaches. Retrieved May 17, 2016, from , H. (n.d.). Image. Retrieved May 17, 2016, from sea cucumbers vegetables? (n.d.). Retrieved May 17, 2016, from , C. Q. (n.d.). Body of Sea Urchin is One Big Eye. Retrieved May 18, 2016, from System. (n.d.). Retrieved May 18, 2016, from sea urchin. (n.d.). Retrieved May 18, 2016, from , B. (2011). Sea urchins may be one gigantic eye - Reef Builders | The Reef and Marine Aquarium Blog. Retrieved May 18, 2016, from Urchins. (n.d.). Retrieved May 18, 2016, from ., C. (n.d.). The Echinoblog. Retrieved May 18, 2016, from Urchin. (n.d.). Retrieved May 18, 2016, from of Natural Curiosities. (n.d.). Retrieved May 18, 2016, from ................
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