Phylum Cnidaria

Classes: We are only going to talk about 4 classes Hydrozoa: Portuguese Man-of-War, hydra, Obelia Scyphozoa: True Jellyfish Cubozoa: Box Jellyfish Anthozoa: Sea anemones, Coral, and Sea fans

Hydrozoa 2700 species Two groups: Hydroids Siphonophores Mainly marine animals Two life stages Polyp (hydra’s only have polyp stage) Medusa Found in mainly in polyp colonies

Scyphozoa 200 Species True Jellyfish Marine coastal waters Two stages Polyp (restricted to small larval forms) Medusa

Cubozoa 20 species Marine coastal water Two Stages Polyp Medusa (dominate stage) Square shaped when viewed from above

Anthozoa 6200 species Marine coastal waters One stage Polyp only Most live in colonies Coral Reef

Characteristics Radial Symmetry

Characteristics Gastrodermis One body opening Two cell layers are organized into tissues with specific functions. The inner layer is adapted mainly to assist in digestion. Oxygen dissolved in water can diffuse directly into body cells. Carbon dioxide and other wastes can move out of a cnidarian’s body cells directly into the surrounding water Gastrodermis

Characteristics Two stages Polyp Medusa One body form may be more observable than the other. In jellyfishes, the medusa is the body form usually observed. The polyp is the familiar body form of hydras

Life Cycle & Reproduction Medusa only life cycle Polyp only life cycle

Life Cycle & Reproduction All cnidarians have the ability to reproduce sexually and asexually. Sexual reproduction occurs in only one phase of the life cycle It usually occurs in the medusa stage, unless there is no medusa stage then the polyp can reproduce sexually Sexual Reproduction Asexual Reproduction sperm egg

Digestion Cnidarians are predators that capture their prey using nematocysts A nematocyst is a capsule that contains a coiled threadlike tube May be sticky or barbed, and it contains toxic substances Nematocysts are located in stinging cells called cnidocytes, on the tentacles

Digestion Hydra eating a daphnia Once captures by nematocysts, prey is brought to the mouth by contraction of the tentacles Prey is moved to the gastrovascular cavity The cells that line the gastrovascular cavity release enzymes over captured prey. Any undigested materials are ejected back out through the mouth.

Nervous system A cnidarian has a simple nervous system without a control center, such as a brain like that of other animals. In cnidarians, the nervous system consists of a nerve net that conducts impulses to and from all parts of the body The impulses from the nerve net cause contractions of muscle-like cells in the two cell layers.