Download Phylum Cnidaria - G. Holmes Braddock High School

Phylum Cnidaria
Jellyfish, Corals, and Sea Anemones
General Characteristics
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Tentacles
Hydrostatic skeleton
Nerve net
Radial symmetry
Saclike 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 Cnidarians
• Medusa – free floating, motile, part of the
plankton, tentacles and mouth point down
• Polyp – sessile, part of the benthic
community, tentacles and mouth point up.
Classes of Cnidarians
• Hydrozoans
– Most are colonial
– Polyp body form for most of its life cycle
– Some do not have a medusa stage others do not
have a polyp stage, but most have both stages in
their life cycle
– Examples: Portuguese Man-o-War, Hydra
• Scyphozoans
– Most are solitary
– Medusa body form for most of its life cycle
– Examples: 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 shape
– Not all species are deadly, but can cause very
painful stings
• Anthozoans
– Only found in the polyp body form
– Reproduce both asexually (budding) and
sexually (shed eggs and sperm into the water)
– Three groups of anthozoans:
• Anemones – soft fleshy polyps, usually solitary
• Soft Corals – sea fan and sea whips
• Hard 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.