Phylum Cnidaria

General Characteristics They are radially symmetrical They have 2 tissue layers: Epidermis - Outer layer of cells Gastrodermis Inner layer which lines the gut cavity or gastrovascular cavity In between these tissue layers is a non-cellular jelly-like material called mesoglea

Cnidarian Body Plans Polyp form Tubular body, with the mouth directed upward. Around the mouth are a whorl of feeding tentacles. Only have a small amount of mesoglea Sessile Medusa form Bell-shaped or umbrella shaped body, with the mouth is directed downward. Small tentacles, directed downward. Possess a large amount of mesoglea Motile, move by weak contractions of body Hydras, sea anemones, corals

Skeletal/Muscle System most have primitive muscle cells; coral have external skeleton of calcium carbonate

Stinging Organelles cnidarians are carnivores (eat meat) that use tentacles arranged in a ring around their mouth to capture prey Prey is captured by using specialized stinging cells called cnidocytes located in the outer epidermis. Each cnidocyte has a modified cilium - cnidocil, and is armed with a stinging structure called a nematocyst. Some nematocysts function to entangle the prey; others harpoon prey and inject a paralyzing toxin.

Digestion Sac w/ a digestive cavity (gastrovascular cavity) w/ a single opening that acts as a mouth/anus Jellyfish Hydra

Digestion (cont.) food is pushed into the gastrovascular cavity where digestion begins (extracellular digestion) undigested remains leave through the mouth/anus

Nervous System Nerve Net- Cnidarians do not have a brain but they have simple sensory receptors that detect & respond to stimuli

Circulation NONE!!

Respiration Diffusion- oxygen from water moves into sponge cells (high to low)

Reproduction Asexual – budding- formation of outgrowths that pinch off from parent to live independently Sexual- forms a zygote and free swimming planula that settles on ocean floor *MOST ALTERNATE B/W POLP & MESDUSA LIFE FORM

Reproduction (cont.)

Excretion mouth/anus- release waste