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Marine Invertebrate Zoology
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Marine Invertebrate Zoology

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  1. Marine Invertebrate Zoology The Hydrostatic Skeleton Phylum Cnidaria Phylum Cnidaria

  2. The Hydrostatic Skeleton Phylum Cnidaria

  3. The Hydrostatic Skeleton • The hydrostatic skeleton requires: Phylum Cnidaria

  4. Phylum Cnidaria Overview • Defining Characteristics • Formation of complex intracellular organelles called nematocysts • Planula larvae in the life cycle • The phylum is composed of anemones, corals, sea whips, hydroids, and jellyfishes • Diploblastic Phylum Cnidaria

  5. Diploblastic Animals • Epidermis • Gastrodermis Phylum Cnidaria

  6. Nematocysts • Used for gathering food or defense • Produced in special cells called cnidoblasts SEM micrograph of nematocysts penetrating skin Phylum Cnidaria

  7. Nematocysts Phylum Cnidaria

  8. Cnidarian Nutrition • A major cnidarian drawback is the absence of an anus • Carnivorous feeders on zooplankton and small fish • Reef building corals also depend on symbiotic photosynthetic dinoflagellates for energy Phylum Cnidaria

  9. Reproduction and Nervous System • Reproduce asexually and sexually • Larvae - mouthless, ciliated, swimming planula • In the classes Scyphozoa and Hydrozoan the sexual stage is the medusa • Alternate between the polyp and medusa • The polyp asexually produces a medusa that sexually produces a planula larvae, which then settles into a polyp • Polymorphism = more than one stage per species Phylum Cnidaria

  10. Polyp & Medusa

  11. Medusa (jellyfish) Usually solitary and free swimming The mouth and tentacles are directed downwards Contains thick mesoglea Polyp (tube shape) Solitary or colonial, usually sessile attached by its base Mouth and tentacles are pointed upward Mesoglea is usually thin May have a fluid skeleton or calcium carbonate exoskeleton Polyp and Medusa Phylum Cnidaria

  12. Cnidarian Classification • Phylum Cnidaria • Class Scyphozoa • Class Cubozoa • Class Hydrozoa • Order Hydroida • Order Siphonophora • Class Anthozoa • Subclass Alcyonaria (Octocorallia) • Subclass Zoantharia (Hexacorallia) Phylum Cnidaria

  13. Class Scyphozoa • Defining characteristic • Asexual replication by strobilation • Includes the true jellies, moon jellies (Aurelia) and Sea Nettles (Chrysaora) Phylum Cnidaria

  14. Scyphomedusa Structure • Contains a large swimming bell that has tentacles and sensory capsules • Rhopalia • Statocysts • Ocelli Rhopalia Phylum Cnidaria

  15. Medusa Movement Phylum Cnidaria

  16. Scyphomedusa Structure Phylum Cnidaria

  17. Scyphozoa Lifecycle

  18. Class Cubozoa • Defining characteristics • Medusa with box-like body • Chiropsalmus quadrumanus (Sea Wasp) Phylum Cnidaria

  19. Class Cubozoa • Known as box jellies or sea wasps due to shape and painful sting • Occur in tropical and warm temperate seas Cubozoa Eyes Phylum Cnidaria

  20. Class Hydrozoa • Due too small sizes and plant-like appearance people are unaware of their existence • Display both polyp and medusa in the life cycle • Mesoglea is thin or absent Phylum Cnidaria

  21. Hydroid Structure • Polyps can be solitary or colonial • Very drab in appearance, no external skeleton, colonies are polymorphic Hydra Phylum Cnidaria

  22. Polymorphism • Hydroid colonies have polyps of different functions • Feeding - gastrozooids • Defense - dactylozooids • Reproduction - gonozooids Phylum Cnidaria

  23. Hydromedusa Structure Phylum Cnidaria

  24. Hydrozoan Reproduction • Hydroid stage can reproduce by asexual budding • Eventually the bud detaches and becomes independent • Also has considerable powers of regeneration • Gonozooids will release medusa • All medusa reproduce sexually Phylum Cnidaria

  25. Hydrozoa Lifecycle

  26. Order Hydroida • Most species of the class hydrozoa in our area are hydroids • Form sessile colonies of polyps and are usually mistaken as seaweed • Exceptions are Velella and Porpita = hydroids that float freely at the surface Velella Phylum Cnidaria

  27. Order Siphonophora • Swimming or floating hydrozoan colonies • Portuguese man-o-war (Physalia physalis) Phylum Cnidaria

  28. Phylum Cnidaria

  29. Class Anthozoa • Defining characteristics • Absence of a medusa stage • Anemones, corals, sea whips, sea pansies • Polyps consists of a column, flattened oral disk surrounding the mouth which bears tentacles • Some polyps are solitary (anemones) others are colonial (coral) Phylum Cnidaria

  30. Class Anthozoa • Feed using tentacles that move food to the mouth • Water is used by some as a fluid skeleton • Produce planula larvae that settle and form new colonies • Can also reproduce using pedal laceration and fission Phylum Cnidaria

  31. Subclass Zoantharia (Hexacorallia) • Posses 6 septa that separate the gastrovascular cavity • Many species are solitary and lack a protective covering (sea anemones) • Separated into two major orders Phylum Cnidaria

  32. Sea Anemones • Solitary and lack a rigid skeleton • Have a broad adherent pedal disk • Can reproduce asexually (pedal laceration) and sexually Phylum Cnidaria

  33. Stony corals • Colonial with calcium carbonate skeleton secreted by the epidermis • May be reef-building (hermatypic) or non reef building (ahermatypic) • Hermatypic corals live in warm clear waters and can form chains around islands • Zooxanthellae forms a symbiotic relationship with coral Phylum Cnidaria

  34. Subclass Alcyonaria (Octocorallia) • Distinguishing characteristics • Sea whips, sea fans, and sea pansies are in this group • Can harbor zooxanthellae Phylum Cnidaria