Cnidarians & Ctenophorans
1
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 Characteristics
• 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 Characteristics
•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
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
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
Hydrozoans
Hydra
•Exist only as polyps
•Reproduce by
budding
•Freshwater only
•Form resistant
zygotes when
environment is bad
•Move by
somersaulting with
tentacles
Hydra
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
Cubozoans
Box JellyFish
Scyphozoans
Scyphozoan
Characteristics
Jellyfish
• Medusa is dominant
body form
• Go through small
polyp stage during
life cycle
•Stinging tentacles
•May live close to
shore or the open
ocean
Parts of a Jellyfish
Jellyfish
Life Cycle
24