Jellyfish, Corals, and Sea Anemones Phylum Cnidaria Jellyfish, Corals, and Sea Anemones

General Characteristics 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.