Cnidarians

1. Cnidarians

2. PhyllumCnidaria Cnidaria: means “nettle.” Includes Jellyfish, Sea Anemones, and Corals Contains 9,000 mostly marine species Carnivorous: eat crustaceans, fishes, worms, and diatoms.

3. 3 Classes • Hydroidea: • Small, polymorphic (can be both medusa and polyps) • Scyphozoa: • Mainly jellyfish • Polymorphic • Anthozoa: • Corals and sea anemones. • Lack medusa stage

4. Cnidoblasts Almost all Cnidarians have stinging cells called cnidoblastsor nematocysts. These cnidoblasts are deployed on tentacles that end or retract toward the mouth. Each cnidoblast has a capsule with a coiled threat that can be forcefully ejected and contains a toxin or immobilizing prey.

5. Digestion The tentacles bring food toward the saclike digestive cavity. Digested food is absorbed by cells of the digestive cavity and transported to other parts of the animal by migratory cells or by diffusion. Indigestible bones are eliminated through the mouth.

6. Morphology Multicelluar Single body cavity called and enteron An opening surrounded by tentacles with stinging cells or cnidoblasts. The opening functions as both the mouth and the anus.

7. Morphology • Three layers of cells: • Inner layer called Endoderm or gastrodermis responsible for digestion and reproduction. • Outer layer called the ectoderm or epidermis for capturing prey and for protection from attack. • Mesogloea: gelatinous, non-living layer holding the other layers together. • Radial Symmetry: Body parts radiate from a central axis. • No cnidarian possesses a definite head or concentration of sensory receptors, but can have a primitive network of nerves. • No excretory or circulatory systems. • Sea anemones and corals are benthic and attach to rocks. Jellyfish are pelagic and float in the water column.