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 buildersPolyp grows in 6 parts to form a body of

calcium carbonateBrain coral and staghorn coral

Soft CoralPolyps 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 anemonecontain powerful nematocysts that cause

skin irritationFire 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 polypsPolyps may be specializedAttach to pilings, shells, seaweed, etc.Siphonophores - hydrozoans that form

drifting colonies (Portugues man of war)

Scyphozoans - Class Scyphozoa

Larger jellyfishBell 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 anemonesStony corals and sea fans

Textbook readings

The case of the killer Cnidarians