Download Phylum Cnidaria - Solon City Schools

Jellyfish, hydra, sea anemones,
& coral
Cnidarian questions
What do we already know about Cnidarians
(from the phlyo. Tree)
1.
1.
Two tissue layers (germ layers)(ecto and endoderm)
1.
2.
“diploblastic”
Radial Symmetry
2. Look at the life cycle of a jellyfish…
A. What are the two body types of Cnidarians?
B. Which is mobile? Sessile?
A.
B.
Medusa is mobile
Polyp is sessile
Appearance
 Polyp: 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.)
Symmetry
 Radial symmetry
Skeletal/Muscle System
 NO 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
Nematocyst
at work
(harpoon)
Cnidocyte
(stinging cell)
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
 No brain or even ganglia, no cephalization, etc
 Nerve Net- have simple sensory receptors that detect
& respond to stimuli
Circulation
 NONE!!
Respiration
 Diffusion- 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 POLYP & MEDUSA LIFE
FORM
Reproduction (cont.)
Reproduction (cont.)
Excretion
 Diffusion 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
•Spend most of the life cycle in the
medusa phase
•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.