Cnidarians & Ctenophorans
copyright cmassengale
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CNIDARIANS
Phylum Cnidaria
• About 9000 species
• Most are marine (jellyfish,
coral, sea anemones,
Portuguese man-of war)
• Hydras are found in
freshwater
• All have arm-like
tentacles
Cnidarian Body Plan
• Radial symmetry
• Hollow gut -Gastrovascular
cavity has single opening
(serves as both mouth and
anus)
• Two tissue layers
(diploblastic)
• Outer epidermis and inner
gastrodermis
Cnidarian Characteristics
•Either tubular or bell
shaped
•Tentacles surround mouth
•Only animal with cnidocytes
(stinging cells) found in the
tentacles
•Nematocyst – coiled,
harpoon-like stinger inside
cnidocyte that shoots out
Cnidarian Feeding
•Cnidocytes contain poison to
paralyze prey
•Tentacles bring food into
mouth
•Inner gastrodermis secretes
digestive juices into
gastrovascular cavity which
digests food and circulates
nutrients
Extracellular Digestion
Food
digested
outside
of cells
Cnidocyte
Coiled nematocyst
Nematocyst
Barbed,
threaded
stinger
capsule’s lid
trigger
nematocyst
Cnidarian Systems
•Have a simple
nerve net &
sensory receptors
•Muscles help in
directional
movement &
capturing prey
mesoglea-filled bell
tentacles
Jellylike
mesoglea
between two
cell layers
supports
cnidarian
Two Main Body Plans of
Cnidarians
UPRIGHT TENTACLES
TENTACLES HANG DOWN
epidermis
Polyp
mouth
mesoglea
gastrodermis
Medusa
Mesoglea THICK
Mesoglea THIN
Cnidarian Diversity
• Scyphozoans:
Jellyfish
• Anthozoans:
Sea anemones
Corals
• Hydrozoans:
Hydra
• Cubozoa
Box Jellies
Cnidarian Diversity
Coral polyps
Sea Anemone
Jellyfish
Coral polyps
Anthozoans
Anthozoan Characteristics
Sea Anemones
 Brightly colored & Resemble
flowers
 Solitary polyps
 Feed on invertebrates & fish
Corals
 Most are colonial
 Build limestone case
 Live as polyps in their case
Sea
Anemones &
Coral
• Exist only as
Polyps
• Clownfish live
in anemone
tentacles
• Corals build a
limestone
case which
build up &
form reefs
ANEMONE
CORAL
Distribution of Coral Reefs
Hydrozoans
Hydrozoans
Hydra
•Exist only as polyps
•Reproduce by
budding
•Freshwater only
•Form resistant
zygotes when
environment is bad
•Move by
somersaulting with
tentacles
Hydra
Hydra Feeding
Food in
Gastrovascular
Cavity
Portuguese
man-of-war
• Colonial Hydrozoan
(not a single
organism
• Tentacles sting
prey such as fish
& humans
• Polyps in colony
feed
• Has gas-filled air
float
Hydrozoan Life Cycle
Most hydrozoans alternate between polyp and medusa
forms, as in the life cycle of Obelia
Obelia Life Cycle (Hydrozoan)
Larva called a planula
reproductive
polyp
male medusa
female medusa
ovum
sperm
zygote
feeding
polyp
polyp
forming
planula
Fig. 25-15a, p.411
Cubozoans
Box JellyFish
Scyphozoans
Scyphozoan
Characteristics
Jellyfish (common)
• Medusa is dominant
body form
• Go through small
polyp stage during
life cycle
•Stinging tentacles
•May live close to
shore or the open
ocean
Some Jellyfish Show
Bioluminescence
Parts of a Jellyfish
Jellyfish
Life Cycle
CTENOPHORANS
Phylum Ctenophora
Characteristics
• Called comb jellies
• All marine
• Approximately 100
species
• May be spherical,
ovoid, or elongated in
appearance
• Bioluminescent
Ctenophoran
Characteristics
• Radial symmetry
• Have eight plates of
fused cilia that
resemble combs
• Move by beating cilia
• Most of the body is
jelly-like mesoglea
• Body & tentacles
covered with sticky
mucus to catch prey
Comb Jelly
Anatomy
Beating Cilia
Ctenophore:
Comb Jelly
Ctenophore
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