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  1. 1. Phylum Cnidaria & Ctenophora (ny-dar’ e-a) & (te-nof’ o-ra) The RADIATE Metazoa
  2. 2. Cnidaria (cnidos=nettle like) <ul><li>9000+ species </li></ul><ul><li>Primary radial or biradial symmetry </li></ul><ul><li>700 million+ year fossil record </li></ul><ul><li>2 Germ layers ectoderm ( epidermis ), endoderm ( gastrodermis ), & mesoglea </li></ul><ul><li>Gastrovascular cavity (extracellular digestion) </li></ul><ul><ul><li>Coelenerata (hollow gut) </li></ul></ul><ul><li>Nerve net (no CNS) </li></ul><ul><li>Locomotion via epitheliomuscular cells </li></ul><ul><li>Polymorphism (one species, multiple forms) </li></ul><ul><li>Nematocysts (unique to Cnideria) </li></ul>
  3. 3. Cnideria contd. <ul><li>Usually shallow marine habitats </li></ul><ul><li>Some on the open ocean or at depth </li></ul><ul><li>Many have bioluminescence. </li></ul><ul><li>Symbiosis : commensals (anemonies), mutuals (zooanthellae) </li></ul><ul><li>More on polymorphism </li></ul><ul><ul><li>Polyps </li></ul></ul><ul><ul><li>Medusae </li></ul></ul>
  4. 4. Life cycle <ul><li>Hydrozoa </li></ul><ul><li>Scyphozoa </li></ul>Medusae are specialized for dispersal. Polyps are specialized for colonial life.
  5. 5. Cnidocytes <ul><li>Cnidoblast (developing) </li></ul><ul><li>Nematocyst </li></ul><ul><li> Osmotic pressure </li></ul><ul><ul><li>Leads to  hydrostatic pressure </li></ul></ul><ul><li>Operculum (covering) </li></ul><ul><li>Cnidocil (trigger) </li></ul><ul><li>Venomous or adhesive </li></ul>
  6. 6. Hydra Cnidocyte
  7. 7. Sometimes nematocysts are stolen and used by other invertebrates. -nudibranchs -comb jellies
  8. 8. Nervous system <ul><li>No CNS </li></ul><ul><li>Nerve net or plexus </li></ul><ul><li>No myelin </li></ul><ul><li>Nerve signals transmitted in both directions at the synapse </li></ul><ul><li>Statocyst (equilibrium) </li></ul><ul><li>Ocelli (simple eyes) </li></ul>
  9. 9. 4 Classes of Cnidaria <ul><li>Hydrozoa (e.g.. hydroids, fire corals, Portuguese man-o-war) </li></ul><ul><li>Scyphozoa (true jellies: e.g.. moon jellies, other bell-shaped jellies ) </li></ul><ul><li>Cubozoa (cube jellies:e.g.. Chironex fleckeri ..or Sea wasp ) </li></ul><ul><li>Anthozoa (e.g.. anemones , stony corals, & soft corals such as sea pens ) </li></ul>
  10. 10. <ul><li>Class Hydrozoa </li></ul><ul><li>Includes the solitary freshwater hydra; Most are colonial and marine </li></ul><ul><li>Typical life cycle includes both asexual polyps and sexual medusa stages; however, freshwater hydras and some marine hydroids do not have a medusa stage. </li></ul><ul><li>Hydras </li></ul><ul><li>Solitary freshwater hydras are found in ponds and streams occurring on the underside of vegetation. </li></ul><ul><li>They possess a pedal disc , mouth on a hypostome , surrounded by 6-10 tenetacles. </li></ul><ul><li>Mouth leads to a gastrovascular cavity* </li></ul><ul><li>Sexual reproduction: Ovaries and testes form on the body wall. Sperm are released into the water, and fertilize eggs within the ovaries. Resulting blastula falls off the parent as a cyst which can last the winter. </li></ul><ul><li>Asexual reproduction: budding </li></ul>* Extracellular & intracellular digestion
  11. 11. <ul><li>Hydrozoa cont. </li></ul><ul><li>Colonial Hydrozoans - e.g., Obelia </li></ul><ul><li>Colonial stalk called hydrocauli </li></ul><ul><li>Skeleton of chitin that is secreted by the epidermis ( perisarc ) </li></ul><ul><li>Two different kinds of individuals or zooids that comprise the colony: feeding polyps called hydranths or gastrozooids and, reproductive polyps or gonangia </li></ul>
  12. 12. <ul><li>Hydrozoa cont. </li></ul><ul><li>Life Cycle of Obelia </li></ul><ul><li>Gonozooids release free swimming medusae. </li></ul><ul><li>Zygotes become planula larvae , which eventually settle to become polyp colonies. </li></ul>Also, the margin of the bell projects inward forming a shelf-like velum. The medusae of hydroids are smaller than those of true jellyfishes ( Scyphozoa ).
  13. 13. Hydrozoa cont. The Portuguese man-of-war (Genus Physalia ) is another example of colonial Hydrozoa . The colony is suspended on a gas-filled floatformed from one of the polyps. The tentacles house the polyps and modified medusae of the colony, including the dactylozooids or “fishing tentacles”. A mutualistic relationship exists between Physalia and a small fish ( Nomeus ) which feeds off of the tentacles.
  14. 14. <ul><li>Class Scyphozoa </li></ul><ul><li>“ Jellyfish” have the most conspicuous medusae. </li></ul><ul><li>The medusae are large and contain large amounts of mesoglea (the jelly) . </li></ul><ul><li>They differ from the hydrozoan medusa in that they lack a velum . </li></ul><ul><li>They possess four gastric pouches lined with nematocysts to further subdue prey. Pouches are connected with the mouth as part of the gastrovascular system. </li></ul><ul><li>They have many rhopalia for sensory function (vision & gravity) </li></ul>Moon Jellyfish
  15. 15. Scyphozoan Life Cycle - Aurelia <ul><li>Gametes develop in the gastrodermis of gastric pouches; eggs and sperm are shed through the mouth. </li></ul><ul><li>Fertilized eggs develop into a planula larva which settles on substrate and develops into a polyp - scyphistoma. </li></ul><ul><li>Scyphistoma produces a series of polyps by budding - Strobila </li></ul><ul><li>The polyps undergo differentiation and are released from the strobila as free swimming ephyra </li></ul><ul><li>Ephyra matures into an adult jellyfish </li></ul>
  16. 16. Illustration from page 266 of the text Aurelia Life Cycle
  17. 17. Class Cubozoa (box jellies) <ul><li>Medusae are the dominant form (2-25cm) </li></ul><ul><li>Good swimmers ( eyes ) </li></ul><ul><ul><li>More ocelli </li></ul></ul><ul><li>Bells are squared (hence box jellies) </li></ul><ul><li>Pedalium at the base of each tentacle </li></ul><ul><li>Polyps small, little known </li></ul><ul><li>Subumbrella forms a velarium similar to a velum in Hydromedusae </li></ul><ul><li>Sting can be severe or even fatal… Sea Wasp </li></ul>
  18. 18. The eye of a box jellyfish, class Cubozoa
  19. 19. <ul><li>Class Anthozoa (anemonies, corals, sea pens, etc.) </li></ul><ul><li>Exclusively marine; there is no medusa stage </li></ul><ul><li>At one or both ends of the mouth is a ciliated groove called the siphonoglyph, which generates a water current and brings food to the gastrovascular cavity </li></ul><ul><li>They possess a well developed pharynx </li></ul>“ Flower” animals The gastrovascular cavity is large and partitioned by septa or mesenteries ; These increase surface area for digestion or support. Edges of the septa usually have acontia threads, equipped with nemat-ocysts that protrude from the mouth and pores for defense and prey capture.
  20. 20. <ul><li>Anthozoa cont. </li></ul><ul><li>Solitary anthozoans include sea anemones </li></ul><ul><li>Most anthozoans are colonial (e.g. corals) and secrete external skeletons composed of calcium carbonate. </li></ul><ul><li>Hexamerous or Octamerous symmetry </li></ul><ul><li>Recognize prey through chem-ical detection (glutathione or asparagine) and vibration freq. </li></ul><ul><li>Many corals obtain much of their energy from microscopic, photosynthetic dinoflagellates ( zooxanthellae ) that live symbiotically inside the cells of the coral. </li></ul>
  21. 21. Reproduction <ul><li>Anemonies </li></ul><ul><ul><li>Monoecious and dioecious </li></ul></ul><ul><ul><li>Protandrous if monoecious </li></ul></ul><ul><ul><li>Asexual reproduction by </li></ul></ul><ul><ul><ul><li>Budding </li></ul></ul></ul><ul><ul><ul><li>Longitudinal fission </li></ul></ul></ul><ul><ul><ul><li>Pedal laceration </li></ul></ul></ul><ul><li>Hard Corals (hexacorallian) </li></ul><ul><ul><li>Sexual repro. </li></ul></ul><ul><ul><ul><li>Moneceous & dioecious </li></ul></ul></ul><ul><ul><ul><li>Spawning </li></ul></ul></ul><ul><ul><ul><li>Planula larva </li></ul></ul></ul><ul><ul><li>Asexual repro. </li></ul></ul><ul><ul><ul><li>Budding </li></ul></ul></ul><ul><ul><ul><li>Fission </li></ul></ul></ul><ul><ul><ul><ul><li>Transverse </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Longitudinal </li></ul></ul></ul></ul>Anthozoa contd .
  22. 22. Coral Reef types ( more ) <ul><li>Fringing reef </li></ul><ul><ul><li>Close to land; narrow or no lagoon </li></ul></ul><ul><li>Barrier </li></ul><ul><ul><li>Parallel to shore; wide, deep lagoon </li></ul></ul><ul><li>Patch </li></ul><ul><ul><li>Located on the leeward side of a barrier reef or atoll </li></ul></ul><ul><li>Atoll </li></ul><ul><ul><li>Encircle a lagoon, but not an island </li></ul></ul><ul><li>Hermatypic (reef building) corals </li></ul><ul><li>Coraline algae </li></ul><ul><li>Shallow water (<30m) & warmth ( + 30° Lat.) </li></ul><ul><li>Large formations of calcium carbonate (CaCO 3 ) </li></ul><ul><li>Tremendous diversity of life (Islands of life) </li></ul>
  23. 23. The little-known fifth class of Cnidaria, the Ostrizoa
  24. 24. Ctenophora ( Comb Jellies ) <ul><li>Colloblasts (glue-secreting cells - prey capture) </li></ul><ul><li>Cilliated Comb rows (swims mouth first) </li></ul><ul><li>Marine, < 100 species; many deep water sp. </li></ul><ul><li>Two tentacles which retract into sheaths </li></ul><ul><li>No nematocysts (H. rubra steals them) </li></ul><ul><li>Aboral organ senses gravity (statocyst) </li></ul><ul><li>Aboral canal voids waste (complete gut) </li></ul><ul><li>Epidermis, gastrodermis, and collenchyme which contains distinct muscle fibers . </li></ul><ul><li>Respiration & excretion through cell membranes </li></ul><ul><li>Bioluminescence </li></ul>
  25. 25. Ctenophora life cycle <ul><li>Monoeceous </li></ul><ul><li>Eggs and sperm released into the water </li></ul><ul><li>Free swimming cydippid larva </li></ul><ul><li>No polyp stage </li></ul>
  26. 26. The End Brought to you by… Hydrozoa & Scyphozoa