Phylum Cnidaria

Jellyfish, hydra, sea anemones,

& coral

Appearance• Polyp: cylindrical, pine shaped

animals that are usually attached to a rock or

Ex. Hydras, sea anemones, corals• Medusa: bell-shaped body; umbrella Ex. Jellyfish *Have 2 tissue layers: ectoderm &

endoderm

Appearance (cont.)

Appearance of a jellyfish

Symmetry

• Radial symmetry

Skeletal/Muscle System

• most have primitive muscle cells; coral have external skeleton of calcium carbonate

Capturing PreyLET’S EAT!!!

• cnidarians are carnivores (eat meat) that use tentacles arranged in a ring around their mouth to capture prey

• when a “trigger” is stimulated on a stinging cell called the cnidocyte, a harpoon or nematocyst shoots out & injects poison into the prey

Capturing Prey: Cnidocyte and Nematocyst at work:

Cnidocyte (stinging cell)

Nematocyst (harpoon)

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) then food is passed to food vacuoles of gastrodermis

• 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 gastrodermal 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; usually have separate sexes (male & female species) but some hermaphrodites do exist

• *MOST ALTERNATE B/W POLYP & MEDUSA LIFE FORM

Reproduction (cont.)

Reproduction (cont.)

Excretion

• mouth/anus- release waste