Phylum Cnidaria or Coelenterata Jellyfish, anemones, corals

The Basics Two tissue layers - an outer epidermis and an inner gastroderm Nerve net with stinging capsules called nematocysts Radial symmetry with 2 body types - a polyp and/or medusa

The coral animal may live as a free-floating polyp or build colonies into reefs. Not all corals build reefs.

Stony Coral Hermatypic or reef builders Polyp grows in 6 parts to form a body of calcium carbonate Brain coral and staghorn coral

Soft Coral Polyps with 8 tentacles While part of the reef, they do not build reefs because their bodies are a soft keratin. Sea fans and gorgonians

Hydrocoral False corals resemble the anemone contain powerful nematocysts that cause skin irritation Fire coral

Some cnidarians exist as individuals and others live as colonies like the Portuguese man-of-war.

It has a gas filled float and individuals that function like specialized organs. Some are carnivores with digestion in food vacuoles.

Cnidarians Class varieties

Hydrozoans - Class Hydrozoa Feathery or Bushy colonies of tiny polyps Polyps may be specialized Attach to pilings, shells, seaweed, etc. Siphonophores - hydrozoans that form drifting colonies (Portugues man of war)

Scyphozoans - Class Scyphozoa Larger jellyfish Bell of some medusae may reach 2 m. Some are the most dangerous in the world

Anthozoans - Class Anthozoa Solitary or colonial polyps that lack a medusa stage. Sea anemones Stony corals and sea fans

The case of the killer Cnidarians Textbook readings The case of the killer Cnidarians