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.