phylum cnidaria. general characteristics they are radially symmetrical they have 2 tissue layers:...
TRANSCRIPT
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.)
Reproduction (cont.)
Excretion
• mouth/anus- release waste