phylum cnidaria jellyfish, corals, and sea anemones

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  • Phylum CnidariaJellyfish, Corals, and Sea Anemones

  • General CharacteristicsTentaclesHydrostatic skeletonNerve netRadial symmetrySaclike digestive system (only one opening for mouth/anus)Two layers of cells with mesoglea (jelly-like material) in between.Lack special organs for respiration, excretion, and have no blood

  • Nematocysts (stinging cells) used for feeding, defense, and some contain toxins.

  • Two Body Forms of CnidariansMedusa free floating, motile, part of the plankton, tentacles and mouth point downPolyp sessile, part of the benthic community, tentacles and mouth point up.

  • Classes of CnidariansHydrozoansMost are colonial Polyp body form for most of its life cycleSome do not have a medusa stage others do not have a polyp stage, but most have both stages in their life cycleExamples: Portuguese Man-o-War, Hydra

  • ScyphozoansMost are solitaryMedusa body form for most of its life cycleExamples: true jellyfish like the Moon Jelly (Aurelia)

  • Cubozoa Box Jellyfish (Sea Wasp)The deadliest jellyfish in the world are a type of box jellyfish, with the typical cube body shapeNot all species are deadly, but can cause very painful stings

  • AnthozoansOnly found in the polyp body formReproduce both asexually (budding) and sexually (shed eggs and sperm into the water)Three groups of anthozoans:Anemones soft fleshy polyps, usually solitarySoft Corals sea fan and sea whipsHard Corals which have a calcareous skeleton (usually) and build coral reefs, usually colonial

  • Most anthozoans have a symbiotic relationship with a dinoflagellate known as zooxanthellae living in their tentacles that produce food for the coral in exchange for a place to live and nutrients.


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