Phylum: Cnidaria (Coelenterata, Ctenophora) Jellyfish, Sea Anemones, Hydriods and Corals Things that Sting!!!!

General Characteristics All Cnidarians contain stinging cells called nematocysts which they use to paralyze and trap prey so that they can move them to their mouth area for digestion. Cnidarians have two body stages: Medusa: free moving planktonic Polyp: non moving sessile

Class: ANTHROZOA Corals & Anemones Corals are invertebrates that are in symbiosis with an algae - that means they exchange nutrients or other services with one another in order for both to survive better. They have an alternation of generations during their life cycle (this cycle alternates from a medusa to a polyp stage). However, the class anthozoa's medusa stage is short and once they fix themselves in one place, they become sessile.

Corals come in all shapes and sizes--some are reef-builders while others are non reef-builders: Reef builders build high structures composed of living and non-living materials. The living materials are most often sponges, algae, and the corals themselves. The non-living materials are most often the discarded shells of dead bivalves (clams, mussels, etc.) and other CaCO3 materials. Coral reefs grow about a meter every one thousand years.

Non reef-builders usually inhabit the bottom of more shallow areas of the ocean. They do not build high structures.

A sea anemone will usually attach itself to rocks or coral A sea anemone will usually attach itself to rocks or coral. They have a central mouth which is surrounded by tentacles with nematocysts, paralyzing and entangle small marine animals. Sea anemones primarily reproduce sexually: They exist only in the polyp stage and obtain their food by filter feeding.

Hydroids & Siphonophores Class: HYDROZOA Hydroids & Siphonophores The animals of the class hydrozoa have both a polyp and medusa stage. Siphonophores are a type of hydrozoan with a float for buoyancy. Probably the most famous of these is the species physalia, the Portugese-man-of-war, which is a type of colonial siphonophore.

Portugese-man-of-war

Class: SCHYPHOZOA Jellyfish Jellyfish are cnidarians which lack the polyp stage of the life cycle. Therefore, they are always in the medusa stage. They are considered plankton because they cannot swim on their own--they are dependent upon the current to take them places