phylum cnidaria jellyfish, corals, and sea anemones

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.