Jellyfish, hydra, sea anemones, & coral
Cnidarian questions1. What do we already know about
Cnidarians (from the phlyo. Tree)1. Two tissue layers (germ layers)(ecto and
endoderm)1. “diploblastic”
2. Radial Symmetry2. Look at the life cycle of a jellyfish…
A. What are the two body types of Cnidarians?B. Which is mobile? Sessile?
A. Medusa is mobileB. Polyp is sessile
AppearancePolyp: cylindrical, vase shaped animals that are usually attached to a rock or sea floor
Ex. Hydras, sea anemones, corals
Medusa: bell-shaped body; umbrella
Ex. Jellyfish
Appearance (cont.)
SymmetryRadial symmetry
Skeletal/Muscle SystemNO MESODERM, so…no real muscles!
most have primitive muscle cells coral have external skeleton of calcium
carbonate
Capturing Prey LET’S EAT!!!cnidarians are
carnivores (eat meat) 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
Cnidocyte (stinging cell)
Nematocyst (harpoon)
Capturing Prey: Cnidocyte and Nematocyst at work
Cnidocyte (stinging cell)
Nematocyst (harpoon)
DigestionSac 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 SystemNo brain or even ganglia, no
cephalization, etcNerve Net- have simple sensory receptors
that detect & respond to stimuli
CirculationNONE!!
RespirationDiffusion- oxygen from water moves into
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 form that settles on ocean floor (usually a polyp)
*MOST ALTERNATE B/W POLP & MESDUSA LIFE FORM
Reproduction (cont.)
Reproduction (cont.)
ExcretionDiffusion to release waste
Class Hydrozoa • Ex- Hydra•both asexual polyps and sexual medusa stages•Spends most of its life in the polyp stage
Reproduction: •Sexual: eggs and sperm are shed into the water and form fertilized eggs; planula is by passed with eggs hatching into young hydras •Asexual reproduction via budding
Class Hydrozoa cont.
Other Hydrozoans
Portuguese man-of-war: Single gas-filled float with tentacles Tentacles house the polyps and modified medusae of the colony
Class Scyphozoa
Jellyfish• The medusae are large and contain massive amounts of mesoglea•Sexual and Asexual reproduction
Class Anthozoa
•include sea anemones and coral
•Exclusively marine; there is no medusa stage
• Most anthozoans are colonial (e.g. corals) and secrete external skeletons composed of calcium carbonate.