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What is a Cnidarian?What is a Cnidarian?
A cnidarian is an A cnidarian is an invertebrateinvertebrate
It uses It uses stinging stinging cellscells to capture to capture preyprey
Examples:Examples:– JellyfishJellyfish– CoralsCorals– Sea AnemonesSea Anemones
Body StructureBody Structure
All cnidarians have the following All cnidarians have the following characteristics:characteristics:– Radial symmetryRadial symmetry– A hollow central cavityA hollow central cavity– Tentacles with stinging cellsTentacles with stinging cells
However, cnidarians can have one of 2 However, cnidarians can have one of 2 different body plans. different body plans. – PolypPolyp– MedusaMedusa
Body PlansBody Plans PolypPolyp
– Mouth opens at Mouth opens at toptop– Vase-shapedVase-shaped– Attached to a Attached to a surfacesurface– Examples: Examples: Hydra, Sea Hydra, Sea
anemone, Coralanemone, Coral
MedusaMedusa– Mouth opens Mouth opens downdown– Tentacles point Tentacles point downdown– Adapted for a Adapted for a
swimming life swimming life – Examples: Examples: JellyfishJellyfish
Activity: Color Code a Activity: Color Code a CnidarianCnidarian
Tentacle
Ectoderm Tentacle
Jelly-like layer (Mesoglea)
Endoderm
Obtaining FoodObtaining Food
Stinging cells inject Stinging cells inject venomvenom which paralyzes which paralyzes the preythe prey– THINK!THINK! – Why are clown fish resistant to the – Why are clown fish resistant to the
toxins given off by sea anemones?toxins given off by sea anemones?
TentaclesTentacles pull the prey into the mouth pull the prey into the mouth
Digestion happens in the Digestion happens in the body cavitybody cavity
Waste is expelled back out through the Waste is expelled back out through the mouthmouth
MovementMovement
Cnidarian movements are directed by Cnidarian movements are directed by nerve cellsnerve cells that that spread throughout the cnidarians body like a spread throughout the cnidarians body like a basketball netbasketball net
Jellyfish Jellyfish swim through waterswim through water
Hydras can be found in freshwater and turn Hydras can be found in freshwater and turn somersaults or use their tentacles to movesomersaults or use their tentacles to move– Watch these Hydra MoviesWatch these Hydra Movies
http://micro.magnet.fsu.edu/optics/olympusmicd/http://micro.magnet.fsu.edu/optics/olympusmicd/galleries/moviegallery/pondscum/coelenterata/galleries/moviegallery/pondscum/coelenterata/hydra/index.htmlhydra/index.html
Sea anemones Sea anemones stretch out, shrink down, and bend stretch out, shrink down, and bend slowlyslowly from side to side from side to side
ReproductionReproduction
AsexualAsexual– Budding is most common in hydras, Budding is most common in hydras,
corals, sea anemones where corals, sea anemones where these these polyps just pull apart forming two new polyps just pull apart forming two new polyps.polyps.
SexualSexual– Can occur during the life cycle of Can occur during the life cycle of
certain cnidarians certain cnidarians such as the jellyfishsuch as the jellyfish
Life on a Coral ReefLife on a Coral Reef
Coral polyps produce a Coral polyps produce a hard, stony hard, stony skeletonskeleton around its soft body once around its soft body once attached to a hard surface.attached to a hard surface.
Coral polyps then continue to Coral polyps then continue to reproduce asexuallyreproduce asexually
Over time, reefs build up from the sea Over time, reefs build up from the sea floor and make floor and make great homes for other great homes for other sea lifesea life
Video QuizVideo Quiz
Watch the following clip:Watch the following clip:– Coral Ecosystems (5:59) Coral Ecosystems (5:59)
There will be a short video quiz There will be a short video quiz following the clip. following the clip.
Make sure to take good notes! You Make sure to take good notes! You can use your notes for the video can use your notes for the video quiz!quiz!