Download Cnidarian part 1 - biology-rocks

Man-o-War
• Not really a jellyfish
• Not a single animal
Cnidarians
Chapter 26-3
Pages 564-569
Coral Reefs
Northern Queensland
2000km long
80km wide
Coral Reefs
• Corals produce skeletons of Calcium
carbonate (CaCO3) or limestone
• Grow in colonies
• Food for animals
• Home for animals
• Pearls and shells
• Softens waves
– Protects shorelines
What is a Cnidarian?
• Soft-bodied animals with stinging tentacles
arranged in circles around their mouth
• Have specialized cells and tissues
• Life cycle has 2 stages:
– Polyp and medusa
Two body forms
• Polyp
• Sessile
• Flower-like
• Medusa
• Motile
• Bell-shaped
Polyp or Medusa?
Anything here that is different
from a sponge?
Polyp
Medusa
Cnidaria vs Porifera
• Has body wall that
surrounds a space
– This space = the stomach,
the gut
(gastrovascular cavity)
– Digestion takes place there
• Body wall has 3 layers:
– Epidermis – outer surface
of cnidaria
– Mesoglea – usually jellolike substance
– Gastroderm – covers the
inner surface
Characteristics of Cnidaria
• Feeding: Mostly Carnivorous + symbiotic
relationships
• Symmetry: Radial
• Movement: Sessile (young), Motile (adult)
• Response: Nerve nets + nematocysts
• Reproduction: asexual and sexual
• Internal Transport: diffusion
• Respiration:
exchange O2/CO2 by
diffusion
• Excretion: diffusion
Feeding
• Carnivorous
– Eat small animals by using
stinging structures called
nematocysts
(located on it’s tentacles)
• Symbiotic relationships
– Tiny photosynthetic protists
grow inside of the gastroderm
– Use cnidarian’s waste (CO2/NH3) to make
oxygen
First animal to
move??
Movement
• Polyp
– Sessile
– Can expand, shrink
– Move tentacles by
relaxing and
contracting epidermal
cells
• Medusa
– Free to move in water
– Relax and contract
epidermal cells can
change the bell-shape
– “closing” the bell
pushes water out of
the jellyfish
– Moves forward
by
jet propulsion
Once Thought As Plants?!
They are creatures so
simple that scientists
once considered them
plants. But they're the
critical group to study,
if you want to
understand motion
and behavior.
-- Jack Costello