7. echinoderms and ascidians


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7. echinoderms and ascidians

  1. 1. Phylum Echinodermata<br />“spiny skin”<br />7000 livingspecies<br />All are marine and none are parasitic<br />Morphologically very diverse<br />5 rayed symmetry, mostly radial<br />Pelago-benthic lifecycle<br />
  2. 2. Phylum Echinodermata<br />Ossicles - Calcite endoskeleton that grow with the animal<br />Three forms:<br />Small articulating plates e.g. Sea stars<br />Large closely joined plates – test e.g. sea urchins<br />Widely separated microscopic plates e.g. sea cucumbers<br />
  3. 3. Phylum Echinodermata<br />Water Vascular System<br />Functions in:<br />Locomotion<br />Respiration<br />Feeding<br />Sensory<br />a network of radial canals, which extend through each of the five extensions of the animal. Each canal has a lateral connection which leads to a tube foot. Internally is the ampulla and externally is the podia<br />
  4. 4. Phylum Echinodermata<br />Water Vascular System<br />
  5. 5. Phylum Echinodermata<br />Mutable collagenous tissue<br />ossicles connected by collagenous ligaments<br />Ligaments are normally "locked" (rigid), but can be temporarily "unlocked" (loosened)<br />mechanical advantage<br />maintain a variety of postures with no muscular effort<br />Under neuronal control<br />
  6. 6. Phylum Echinodermata<br />Other Characteristics<br />Pentaradial body organization in adults but all larval forms are biradial<br />Deuterostome embryology (same as humans)<br />No excretory organs<br />No brain<br />Decentralized nervous system consisting of a central nerve ring surrounding the gut, composed primarily of fiber tracks connecting the radial nerves<br />
  7. 7. Phylum Echinodermata<br />StelleroideaEchinoideaHolothuroidea<br />AsteroideaOphiuroidea<br /> Sea Stars Brittle Stars Sea Urchins Sea Cucumbers<br />
  8. 8. Phylum EchinodermataStelleroidea – Ophiuroidea<br />Brittle Stars e.g. Ophiopholis sp<br />~ 2000 living species<br />5 very flexible arms and central body disk<br />Arms are for movement, tube feet (without suckers) are for food gathering<br />Filter feeders, carnivores, scavengers, deposit feeders<br />Arms break off easily (for defense?) - regenerative<br />
  9. 9. Phylum EchinodermataStelleroidea – Ophiuroidea<br />The disk contains all of the internal organs for digestion (mouth and stomach no intestine or anus) and reproduction both tissues never enter the arms, as they do in the Sea stars. <br />
  10. 10. Phylum EchinodermataStelleroidea – Ophiuroidea<br />The underside of the disc contains the mouth. The madreporite is usually located within one of the jaw plates, and not on the upper side of the animal as it is in sea stars<br />
  11. 11. Phylum EchinodermataStelleroidea – Ophiuroidea<br />Nervous system consists of a nerve ring in the disc that sends out a radial nerve to each arm.<br />Lack eyes but the epidermis is sensitive to light and other stimuli.<br />
  12. 12. Phylum EchinodermataStelleroidea – Ophiuroidea<br />Gonochoristic<br />Indirect development with a planktotrophic, ophiopluteus larva<br />A few brood embryos by retaining eggs in the bursa. Sperm enter the bursa and fertilization occurs. Embryos undergo direct development in the bursae and become tiny brittle stars before they are released. <br />
  13. 13. Phylum EchinodermataStelleroidea – Asteroidea<br />Sea Stars e.g. Henricia sp.<br />~ 1500 living species<br />Range from 2 cm to 1 m in size<br />Can live up to 35 years<br />Most have five arms (but as many as 40) with a central disc.<br />Scavengers and carnivores<br />
  14. 14. Phylum EchinodermataStelleroidea – Asteroidea<br />Movement via tube feet (~2000 usually). <br />Internal muscle contractions squeeze fluid to the tube feet, which then elongate<br />The end of the tube feet have suckers, which chemically adhere to or release from the substrate. <br />
  15. 15. Phylum EchinodermataStelleroidea – Asteroidea<br />Aboral surface covered by a thin epidermis covering short spines, pedicellaria and papulae.<br />Papulae and Tube feet have respiratory and excretory functions.<br />
  16. 16. Phylum EchinodermataStelleroidea – Asteroidea<br />e.g. Pycnopodia sp.<br />The non-centralized nervous system allows echinoderms to sense their environment from all sides. Sensory cells on the epidermis sense light, contact, chemicals and water currents. <br />
  17. 17. Phylum EchinodermataStelleroidea – Asteroidea<br />Several long, narrow sensory tube feet extend from the tip of each arm have chemo- and mechanoreceptors. <br />At the tip of the arm is a small circle of short, blunt movable spines that surround a small, pale red or yellow eyespot<br />
  18. 18. Phylum EchinodermataStelleroidea – Asteroidea<br />They feed by grasping the prey, then everting their stomach and secreting primary enzymes on the prey. The digestive juices break down the tissue of the prey, which the asteroids then suck up.<br />
  19. 19. Phylum EchinodermataStelleroidea – Asteroidea<br />
  20. 20. Phylum EchinodermataStelleroidea – Asteroidea<br />The hemalsystem<br />the least understood of echinoderm organ systems. <br />It is a blood vascular system as a space in the connective tissue. But: <br />blood vessels end blindly<br />there is no continuous circulation of blood.<br />
  21. 21. Phylum EchinodermataStelleroidea – Asteroidea<br />e.g. Pisaster sp<br />Reproduction<br />Gonochoristic<br />Fertilization is external. <br />Each individual has a pair of gonads in each arm <br />Every gonad connects to its own gonopore(aboral, base of arm) via an inconspicuous gonoduct<br />
  22. 22. Phylum EchinodermataStelleroidea – Asteroidea<br />two larval forms:<br />Bipinnaria<br />Brachiolaria<br />The larvae are planktotrophic, ciliated, bilaterally symmetrical and feed on diatoms.<br />
  23. 23. Phylum EchinodermataStelleroidea – Asteroidea<br />Adult pheromones<br />may attract larvae, which tend to settle near conspecificadults.<br />May trigger Metamorphosis. <br />A few hermaphroditic species brood their eggs. <br />e.g. Leptasterias sp. <br />
  24. 24. Phylum EchinodermataEchinoidea<br />Sea Urchins, Sand Dollars<br />~ 950 living species<br />Fused ossicles forming thin plates<br />Pentamerouslyradially symmetrical<br />Movable spines vary in size and shape. <br />Tube feet are the major respiratory organs. <br />
  25. 25. Phylum EchinodermataEchinoidea<br />Classified as Regular<br />e.g. Strongylocentrotus<br />radial symmetry,<br />nearly spherical bodies, <br />long spines<br />tube feet are longer than the spines<br />Mouth oral, anus aboral<br />Most are epifaunal. <br />
  26. 26. Phylum EchinodermataEchinoidea<br />Classified as Irregular<br />e.g. sand dollars, Dendraster sp.<br />usually infaunal in soft sediments <br />body is usually flattened<br />spines short<br />Mouth is oral, anus at the edge of the test<br />Reduced aristotle’s lantern<br />
  27. 27. Phylum EchinodermataEchinoidea<br />Aristotle's lantern, equipped with five strong teeth, used for scraping food from hard substrates. <br />40 skeletal ossicles and 60 muscles that support and operate the teeth.<br />
  28. 28. Phylum EchinodermataEchinoidea<br />The tube feet are used for locomotion and respiration, and some use them to hold bits of shell or vegetation above the body, presumably for camouflage or protection from UV radiation in shallow water<br />
  29. 29. Phylum EchinodermataEchinoidea<br />Pedicellariae<br />have three tiny jaws at the end of a pedicle<br />have a skeleton consisting of three ossicles in the jaws and a long slender ossicle in the pedicle<br />
  30. 30. Phylum EchinodermataEchinoidea<br />
  31. 31. Phylum EchinodermataEchinoidea<br />Reproduction<br />Gonochoristic<br />Gametogenesis<br />regulated by photoperiod so that spawning of most or all members of a population occurs during the same time.<br />
  32. 32. Phylum EchinodermataEchinoidea<br />Reproduction<br />Some brood their young externally, within the protection of their spines or tube feet. <br />In species with indirect development, an  echinopluteuslarva is produced. <br />
  33. 33. Phylum EchinodermataHolothuroidea<br />Sea Cucumber<br />1100 living species<br />1 cm – 1 m long<br />Live for 5to 10 years<br />Closely related to echinoideaexcept<br />have tiny ossicles,<br />they are elongated<br />lye on the side of the body<br />madreporiteis internal<br />
  34. 34. Phylum EchinodermataHolothuroidea<br />e.g. Cucumaria sp.<br />Cucumbers are radially symmetrical but also possess a superficial bilateral symmetry in which the oral end is also the anterior end. The aboral end is also the posterior end<br />
  35. 35. Phylum EchinodermataHolothuroidea<br />The anterior (oral) end bears mouth and a circle of ten branched tentacles, the buccalpodia. It is an introvert that can be fully retracted into the body by a set of powerful retractor muscles.<br />
  36. 36. Phylum EchinodermataHolothuroidea<br />
  37. 37. Phylum EchinodermataHolothuroidea<br />Chemosensory and mechanosensory receptors are present in the epidermis and they exhibit a general sensitivity to light but have no special photoreceptive organs. <br />e.g. Eupentacta sp.<br />
  38. 38. Phylum EchinodermataHolothuroidea<br />Podia, which are the external portion of the tube feet, may, be suckered, reduced, or lost. Podia are more randomly scattered along the body than in other echinoderms<br />e.g. Psolus sp.<br />
  39. 39. Phylum EchinodermataHolothuroidea<br />Respiratory trees, which branch out near the rectum of the animal are used for gas exchange as water is pumped through the anus. The respiratory trees are part of the organs that are expelled occasionally by the sea cucumber<br />
  40. 40. Phylum EchinodermataHolothuroidea<br />Reproduction<br />Gonochoristic<br />Broadcast spawners<br />The larvae are planktotrophic<br />Two larval forms<br />Auricularia <br />Doliolaria<br />Adult pheromones may attract larvae to settle near conspecific adults.<br />
  41. 41. Phylum EchinodermataHolothuroidea<br />~ 30 brooding species. Some capture eggs with tentacles, placing the eggs at the sole or dorsal body surface for incubation. A few have internal fertilization and development, where hatched young are released<br />
  42. 42. Phylum EchinodermataHolothuroidea<br />Chemical stimulation<br />changes the mechanical properties of the dermal portion of the sea cucumbers<br />allows the animal to<br />become flexible and squeeze through narrow passages<br />become so rigid that it cannot be dislodged. <br />e.g. Parastichopus sp<br />
  43. 43. Phylum EchinodermataHolothuroidea<br />Eviscerate<br />expelltheir organs, which are later regenerated. This is a seasonal event, but is also thought to be an anti-predator defense.<br />
  44. 44. Phylum EchinodermataHolothuroidea<br />All are filter feeders or deposit feeders moping up sediments from the ocean floor.<br />