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Cnidarians Part Deux

Cnidarians Part Deux. HW:. Reproduction. Most cnidarians have two forms: Polyp – tube shaped body with a mouth surrounded by tentacles Medusa – umbrella shaped body and tentacles that hang down. The mouth is on the ventral side between the tentacles. Reproduction.

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Cnidarians Part Deux

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  1. CnidariansPart Deux HW:

  2. Reproduction • Most cnidarians have two forms: • Polyp – tube shaped body with a mouth surrounded by tentacles • Medusa – umbrella shaped body and tentacles that hang down. The mouth is on the ventral side between the tentacles.

  3. Reproduction • The two forms of cnidarians can be seen in the life cycle of a jellyfish: • The dominant form varies depending on the type of cnidarian.

  4. Jellyfish Reproduction • To reproduce jellyfish (in the medusa stage) release egg and sperm into the water. • When the two meet fertilization occurs – in the water not internally. • Resulting zygotes (product of fertilization) will develop into free-swimming larvae that will grow into polyps.

  5. Jellyfish Reproduction • Jellyfish polyps reproduce asexually to form new medusae (plural of medusa). • So jellyfish alternate generationally from the polyp stage and the medusa stage. • What does this mean???

  6. Cnidarian Diversity • You know that jellyfish and sea anemone’s are cnidarians, but what else is there? • Hydroids • Jellyfishes • Sea Anemone & Coral • How do these three groups consititute 10,000 species????

  7. Hydroids • Hydroids: • ~ 2700 species • Have both polyp and medusa stages in their life cycles. • Most form colonies (like the Portugese Man of War). • Another example of hydroids is the hydra – which we will study.

  8. Jellyfishes • Jellyfishes: • ~200 species • Transparent/transulscent appearance • Medusa is the dominant form, but there is a polyp stage • One well known example is the box jellyfish. • Box jellyfish get their name because the medusa form has a boxlike structure. • A sting from a box jellyfish can kill a human.

  9. Sea Anemones & Corals • ~ 6200 species (WOW) • Polyp stage is the dominant stage. • Recent research suggests bilateral symmetry for the polyps, unlike jellyfish and hydroids.

  10. Sea Anemones & Coral • Sea anemones live as individuals and coral lives in colonies. • Coral secretes calcium carbonate to protect itself. • This creates a hard shell around their soft bodies. • As you may know coral reefs are endangered. • Their health depends on: proper water temperature, adequate light, and appropriate water depth. • Rises in water temperature & pollution pose a threat to this pretty cnidarian.

  11. Summary • The notes from the past two days have described the body structure, digestive & nervous systems, reproduction, and diversity of cnidarians. • You need to read & study these notes in addition to completing the labs and color plates!!!! • REMINDER: DO NOT WRITE IN THE COLOR PLATE BOOKS!!!

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