Transcript 4. Phylum - Cnidaria

Phylum Cnidaria
• About 9000 species
• Most are marine
(jellyfish, coral, sea
anemones)
• Hydras are found in
freshwater
Acad
Body Plan
• Radial symmetry
• Gastrovascular cavity Hollow gut with single
opening (serves as both
mouth and anus)
• Referred to as a twoway digestive system
• The mouth is surrounded
by flexible tentacles
Body Plan
• Two tissue layers: outer
epidermis and inner
gastrodermis
• A jellylike material called
mesoglea is between the
layers
Two Main Body Plans of
Cnidarians
UPRIGHT TENTACLES
TENTACLES HANG DOWN
epidermis
Polyp
mouth
gastrodermis
Medusa
Motile Swimmers
Sessile Filter-feeders
Feeding & Digestion
•Tentacles surround mouth
•Cnidocytes (stinging cells)
found in the tentacles; give
defense and capture prey
•Some work like a harpoon
•Some work like a whip
•Nematocyst – coiled,
harpoon-like stinger inside
cnidocyte that shoots out
Feeding & Digestion
•Cnidocytes contain poison to
paralyze prey
•Tentacles bring food into
mouth
•Inner gastrodermis secretes
digestive juices into
gastrovascular cavity; digests
food and circulates nutrients
•Waste is expelled back
through mouth
Nervous System
•No central
nervous control
•Nerve net &
sensory receptors
•Muscles help in
movement,
reaction to
stimuli, &
capturing prey
Reproduction
• Many can regenerate
(regrow) lost body parts
through mitotic cell
division (asexual)
• Many also reproduce
asexually by budding
Reproduction
• Most reproduction is
sexual
• Many alternate between
medusa and polyp form
in a reproductive life
cycle
Cnidarian Classes
• Hydrozoans:
Hydra
Portuguese man-of-war
• Cubozoa:
Box Jellies
• Scyphozoans (means “cup animals”):
Jellyfish
• Anthozoans (means “flower animals”):
Sea anemones
Corals
Hydrozoans
Hydra
•Exist only as single
polyps
•Freshwater only
Portuguese man-ofwar
• Colonial mix of polyps and
medusas (not a single
organism)
Cubozoans
Box JellyFish
Sea Wasp
– can be
deadly
Scyphozoans - Jellyfish
Anthozoans:
Sea
Anemones &
Coral
ANEMONE
CORAL
Phylum Ctenophora
• Called “comb jellies”
• All marine animals
with radial symmetry
• Approximately 100
species
• May be spherical,
ovoid, or elongate in
appearance
• Bioluminescent
Beating Cilia
Ctenophore:
Comb Jelly
Ctenophoran
Characteristics
• Radial symmetry
• Have eight plates of
fused cilia that
resemble combs
• Move by beating cilia
• Most of the body is a
jelly-like substance
called mesoglea
• Body & tentacles
covered with sticky
mucus to catch prey