Transcript Sea Stars
“Spiny Skin” ~7,000 species Sea stars, sand dollars, and sea urchins A thin skin covers a hard calcareous platelike exoskeleton. Clip • They are divided into six classes: – – – – – – Asteroidea (sea stars) Ophiuroidea (brittle stars) Echinoidea (sea urchins and sand dollars) Crinoidea (sea lilies and feather stars) Holothuroidea (sea cucumbers) Concentricycloidea (sea daisies) Major Characteristics All are aquaticmarine Tube feet:“suction cup” locomotion, feeding, and gas exchange. Sand dollars and sea urchins have moveable spines. Animation The bulb at the top of the tube foot is called the ampulla. •Have water vascular system •A network of hydraulic canals which branch into extensions (tube feet) •Open to the outside through the madreporite plate. Usually body in multiples of five All have an endoskeleton consisting of calcareous plates bearing spines • Bilaterally symmetrical larvae metamorphose into radial adults. -larva of the starfish Feeding: •Various methods Sea Star: Pushes stomach out through its mouth (which is on the underside) into a clam and then digests. Waste excreted through the anuswhich is on top. Obtain oxygen through diffusion • Sea urchins and sand dollars have no arms, but they do have five rows of tube feet that are used for locomotion. – Sea urchins can also move by pivoting their long spines. – The mouth of an urchin is ringed by complex jawlike structures adapted for eating seaweed and other foods. – Sea urchins are roughly spherical, while sand dollars are flattened and disk-shaped. • Sea stars and some other echinoderms can regenerate lost arms and, in a few cases, even regrow an entire body from a single arm. • Sea lilies -attached to the substratum by stalks and • Feather stars -crawl using their long, flexible arms. • Both use their arms for suspension-feeding. • Sea cucumbers • They lack spines, the hard endoskeleton is much reduced in most. • Some tube feet around the mouth function as feeding tentacles for suspension-feeding or deposit feeding •Ecology: •Major food source for other marine animals •Carnivorous echinoderms help control populations of clams •“Crown of Thorns” sea star destroys coral reef systems. • • • • • Echinoderms A. Echinoderms Have a Spiny Skin 1. About 6,000 species of echinoderms are in phylum Echinodermata. 2. Modern echinoderms are all marine. 3. All have an endoskeleton consisting of calcareous plates bearing spines. 4. Class Crinoidea includes 600 species of crinoids; includes stalked sea lilies and motile feather stars. 5. Class Holothuroidea has 1,500 species of sea cucumbers; they have a long leathery body and feed by tentacles about the mouth. 6. About 950 species of sea urchins and sand dollars are in class Echinoidea; they possess spines for locomotion, defense, and burrowing. 7. About 2,000 species of brittle stars are in class Ophiuroidea; they have a central disk from which long, flexible arms radiate. 8. Class Asteroidea contains 1,500 species of sea stars (starfishes). B. Sea Stars 1. Sea Stars are common along rocky coasts; they feed on clams, oysters, and other bivalves. 2. Five-rayed body has an oral (mouth) and aboral (upper) side. 3. Various structures project through the body wall. a. Spines project from the endoskeletal plate through the thin dermis. b. Pincer-like pedicellarie keep the surface free from particles. c. Gas exchange is conducted by skin gills. d. On the oral surface, each arm has a groove lined with tube feet. 4. Sea stars feed by everting the stomach. a. A sea star positions itself over a bivalve and attaches tube feet to each side of the shell. b. Working tube feet alternatively, it pulls a shell open; a small crack allows it to insert a cardiac stomach. c. Stomach enzymes begin digestion of a bivalve while it is trying to close its shell. d. Partially digested food is taken into a pyloric stomach for full digestion. e. A short intestine opens at the anus on aboral side. 5. In each arm is a developed coelom containing paired digestive glands and male or female gonads. 6. Nervous system is a central ring with radial nerves in each arm. 7. A light-sensitive eyespot is at the end of each arm. 8. Locomotion depends upon a water vascular system. a. Water enters on aboral side through a sieve plate (madreporite). b. Water passes through a stone canal to a ring canal and into radial canals in each arm. c. Radial canals feed into lateral canals extending into tube feet; each has an ampulla. d. Contraction of an ampulla forces water into the tube foot, expanding it; when the foot touches a surface, the center withdraws forming a suction and adhering to surfaces. 9. Echinoderms lack a complex respiratory, excretory, or circulatory system. a. Fluids within a coelomic cavity diffuse substances and gases. b. Gas exchange occurs across skin gills and tube feet. c. Nitrogenous wastes diffuse through coelomic fluid and across a body wall. d. Cilia on a peritoneum lining the coelom keep coelomic fluid moving. 10. Sea stars reproduce both sexually and asexually. a. If body is fragmented, each fragment can regenerate a whole animal. b. Sea stars spawn and release either eggs or sperm at the same time. c. The bilateral larvae undergoes metamorphosis to become a radially symmetrical adult. System Type Echinoderm System MuscularSkeletal A Echinoderm has an inner skeleton. It travels by means of many tube feet. Digestion A Echinoderm has a mouth and stomach area. Some have a mouth on the bottom and an anus on the top.Starfish can actually turn their stomachs outside of their body and insert it into its prey's such as a clam. Echinoderms have a relatively big gut area. Nervous A Echinoderm has eyespots which can detect light. Their eyespots are not as sharp as human eyes. It generally has a poorly developed nervous system. Circulation A Echinoderm has water pumped through its body as part of its very simple circulation system. Respiration A Echinoderm uses some of the bumps or spines on its surface to take in oxygen. It has a gill structure to take in the oxygen. It has a poorly developed respiratory system. A Echinoderm is a male or female. The males and females discharge their eggs and sperm into the water where they are fertilized. A female can Reproduction release one hundred million eggs at once. If a piece of certain echinoderms is chopped off, a new piece or even a new echinoderm can regrow. Excretion A Echinoderm has a simple excretory system. Symmetry A Echinoderm has radial symmetry.