Phylum Cnidaria General Characteristics: – Cnidarian means “stinging creature.” – Radial symmetry – Two different body plans exist: medusa and polyp – Cnidarians are made up of two tissue layers separated by mesoglea. Habitat: aquatic

Phylum Cnidaria Nutrition: Capture pray using cnidocytes (stinging cells). – Sting prey and paralyze it so that it can be pulled into the mouth to be digested. – Some organisms become immune to the sting and form mutualistic relationships with cnidarians.

Phylum Cnidaria Digestion: takes place in the gastrovascular cavity, a digestive chamber with one opening, food enters here. – Break down occurs in the cavity and then partially digested food is absorbed by the gastroderm and digestion is finished intracelluarly.

Phylum Cnidaria Circulation: takes place through diffusion in the gastrovascular cavity Respiration: Diffusion of oxygen and carbon dioxide takes place in the gastrovascular cavity. Excretion: diffusion through the body wall or exits out through the mouth of the organism.

Phylum Cnidaria Nervous: – Touch sensitive stinging cells called nematocysts – a nerve net, but no brain – statocysts used to detect gravity – ocelli to detect light (eyespots)

Phylum Cnidaria Reproduction: – Sexual reproduction occurs through external fertilization when the sperm is united with an egg outside of the body

Phylum Cnidaria Reproduction: – Asexual reproduction can occur through budding and fission.

Phylum Cnidaria Examples: sea anemones and coral have a dominant polyp stage, hydra alternate between forms, jellyfish and sea wasps (box jelly) with a dominant medusa form