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Cnidaria

Cnidaria. Dissection Guide Slide study guide. Cnidaria. Diploblastic; endoderm & ectoderm separated by mesoglea Radial symmetry Presence of cnidae/nematocysts in cnidocytes (stinging cells) (see photo at right) Alternation of polyploid (polyp) and medusoid generations

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Cnidaria

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  1. Cnidaria Dissection Guide Slide study guide

  2. Cnidaria • Diploblastic; endoderm & ectoderm separated by mesoglea • Radial symmetry • Presence of cnidae/nematocysts in cnidocytes (stinging cells) (see photo at right) • Alternation of polyploid (polyp) and medusoid generations • Gastrovascular cavity with single mouth/anus • Tissue grade organization • Additional Classes not represented in lab: • Cubozoa: box jellies and sea wasps. • Staurozoa: stalked jellyfish. • Myxozoa: spore-producing parasites

  3. Class Hydrozoa — Hydroids • Alternation of generations: polypoid generation usually dominant • Medusae usually small, transparent • A few (fire corals) produce coral-like calcareous skeleton • Polyps usually colonial, with interconnected coelenterons • No cells in mesoglea • Nematocysts only in epidermis (not gastrodermis) • Marine and fresh waters

  4. Hydra

  5. Hydra

  6. Hydra with developing ovaries Hydra with ovaries and buds

  7. Hydra with developing testes (spermaries)

  8. Hydra Nerve Net neurite neuron

  9. Obelia

  10. Class Anthozoa — Anemones & Corals • Lack medusoid stage • Polyps solitary or colonial • Coelenteron (gastrovascular cavity) subdivided by longitudinal folds of tissue • Tentacles in multiples of 6 (Hexacorallia) or 8 (Octocorallia) • Marine only

  11. Subclass Hexacorallia (Zoantharia)Order Actiniaria • Anemones • Polyps large, usually with distinct stalk • Numerous tentacles • Lack calcified skeleton • Solitary or in aggregations but not truly colonies

  12. acontia

  13. Oral surface of the sea anemone showing the tentacles, mouth and siphonoglyphs.

  14. Cross section through a Metridium looking towards the oral opening - shows complete and incomplete septa.

  15. Detail of the oral opening of the sea anemone showing the position of the siphonoglyphs.

  16. Internal anatomy of the sea anemone - showing the body wall

  17. Cross section through the middle of a sea anemone- Shows complete and incomplete septa.

  18. Cross section through a Metridium looking towards the basal disc - shows complete and incomplete septa.

  19. Longitudinal section of a sea anemone showing the internal anatomy

  20. Internal anatomy of the sea anemone - showing the pharynx and the acontia attached to the base of the cavity

  21. Internal anatomy of the sea anemone showing the acontia

  22. Mesoglea siphonoglyphs

  23. Metridium- Cross section of the anemone, slide, showing the body wall incomplete septa and trilobed ends.

  24. Order Scleractinia • Stony corals • Secrete calcareous skeleton • Most colonial with small polyps, though some solitary • But some solitary with large polyps

  25. Order Alcyonacea • Soft corals • Lack rigid skeleton • Support provided by calcareous spicules • Colonies often tree-like or resemble anemone

  26. Order Gorgonacea • Sea whips and sea fans • Small polyps form branching • Skeleton usually proteinaceous • Sometimes included within the Alcynonacea colonies

  27. Class Scyphozoa — Jellyfish • Medusoid stage predominates; polyps inconspicuous • Thick gelatin-like mesoglea • Often pigmented

  28. Aurelia

  29. Rhopalium of Aurelia

  30. Rhopalium of Aurelia

  31. Rhopalium

  32. Aboral surface is concave and resembles a large sucker. This suction assists the animal in maintaining contact with the substratum. With it the jellyfish can remain in place on smooth vertical surfaces as you have observed in the aquarium.

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