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Phylum Cnidaria
Hydra, jellyfish, coral, & sea
anemones
Phylum Cnidaria
Examples?
• Sea anemones
• Corals
• Sea Pen
• Sea Fan
• Sea Plume
• Hydra
• Jelly fish
• Portuguese Man o’ War
• Box Jelly Fish
I. Body Structure
A. Polymorphism =
more than one body form
1. Polyp
2. Medusa
B. Polyp
• Tube with tentacles
around the mouth
• Mouth pointing in
upward direction.
• Sessile (coral)
Coral polyp
Polyp (sea anemone)
Mythical Hydra
Polyp (Hydra)
Perseus slays the Gorgon Medusa
C. Medusa
• Umbrella shape
• Tentacles around mouth
• Mouth pointing downward
• Motile, Free-swimming
• Have
D. Tentacles
nematocysts
(stinging cells)
• Coiled thread
discharges
like a
harpoon
• Contains
neurotoxin
• Paralyzes
prey
Discharged
nematocyst
Tentacles
• Cnidocytes: epidermal cells which are
used for attachment, defense, and
feeding.
• May contain dischargeable nematocysts –
long tube armed with spines used to
penetrate prey
e. Cnidarian Life Cycle
Stage 1 – Adult Medusa Stage 2 – Planula larva
Stage 3 - Polyp
Discharged nematocyst
II. Level of Organization
A. Tissue
B. No organs
III. Symmetry
Radial
Compass jellyfish
IV. Habitat
A. Aquatic
1. Most Marine
2. Few fresh-water
V. Feeding
A. Carnivores
Lion’s mane eats
(predators)
another jelly
B. Process of feeding
1. Tentacles sting prey with
nematocysts
2. Tentacles grab prey
3. Prey pulled into mouth
Process of feeding
4. Prey stuffed into gastro-vascular
cavity (GVC)*
5. GVC makes enzymes, extracellular digestion
6. Undigested food back out mouth
*incomplete digestive tract (no anus)
Feeding
• Gastrodermis – inner tissue layer derived
from endoderm. Cells used for food
gathering, digestion, and absorption.
Lion’s mane jellyfish eating
VI. Respiration
• Via diffusion
• Body is two cell layers
thick
VII. Internal Transport
Via diffusion
VIII. Excretion
• Via diffusion
IX. Response
A. No cephalization or nervous system
B. Nerve net around mouth
IX. Response
C. Sensory cells
1. Chemoreceptors (chemicals)
2. Thigmoreceptors (touch)
3. Photoreceptors (light)
Ocelli (eyespots)
4. Statocysts (balance)
Response
• Rhopalium – sensory receptors in the
notches at the margin of the medusa in
Aurelia (olfactory, statocyst,
photoreceptors)
• Nerve Ring – encircles the margin of the
medusa in Gonionemus
X. Locomotion
A. Medusa motile, free-swimming
B. Polyps sessile
Exceptions:
1. Hydra tumbles on tentacles
2. Sea anemones glide on pedal disc
XI. Reproduction
1. Asexual
budding from polyps or medusae
2. Sexual
a. Medusae release sperm & eggs
b. Some monoecious, some dioecious
c. Larvae free-swimming
Reproduction
• Gonads – reproductive organs
XII. Ecological Role
A. Predators and prey
B. Neurotoxins in medical research
C. Coral – jewelry, building, reefs (surfing!)
D. Coral reefs - habitat for many
-great biodiversity
- protect coastline
E. Symbiosis with other organisms
Cnidaria Body
Structure
Cnidaria Body Structure
• Manubrium – tubelike structure that hangs
from the medusa’s oral surface (mouth is
found at the end).
• Mesoglea – jellylike layer found between
the two tissue layers (epidermis and
gastrodermis).
Cnidaria Body Structure
• Hydrostatic skeleton – water or body fluids
confined in a cavity of the body and
against which contractile elements of the
body wall act.
• Statocyst – a small sac surrounding a
calcium carbonate structure- “Stone”
moves in response to the pull of gravity,
initiating nerve impulses.
Cnidaria Body Structure
• Tentacle – surrounds the mouth. Used for
catching prey; contains nematocysts.
• Mouth – Points downward in medusa
form. Upward in polyp form. Food enters
through mouth.
• Oral disc – area surrounding mouth.
Contains openings which permit water to
circulate.
Anthozoan Polyp Body Structure
• Pedal Disc – found on the bottom of
anemones. For some, it is used to glide,
but it is also used for asexual reproduction
when a piece separates.
• Pharynx – connects the mouth to the
gastrovascular cavity.
• Acontia – “Threads” found at the end of
mesenterial filaments which contain
cnidocytes. Subdue live prey in the
gastrovascular cavity.
Class Anthozoa: Sea Anemones
Sea Anemones (with sea urchins)
Sea Anemones Clown fish with sea
anemone
Clown fish & eggs with sea
anemone
Clown fish with sea anemone
Giant Sea Anemone
Rosy Sea Anemone
Class Anthozoa: Corals
Brain Coral
Coral
Colt Coral
Elkhorn Coral
Cabbage Coral
Flower Coral
Feather Coral
Gorgonian Fan Coral
Lamellina Coral
Sun Coral
Subergorgia Coral
Soft Coral
Sea Pen
Sea Fan
Sea Plume
Class Hydrozoa: Green Hydra
Hydra
Brown Hydra with buds
Brown Hydra eating
Hydra eating Daphnia
• Hydra eats Daphnia
Class Scyphozoa: True Jellyfish
Fried egg jelly
Jellyfish
Jellyfish
Red-eyed medusa
Jellyfish
Jellyfish
Jellyfish
Lion’s mane
Jellyfish
Purple lion’s mane
Upside down Jelly fish
Upside down Jelly fish
Sea Nettle
Jelly and diver
Giant Jelly off Coast of Japan
Beached Jelly fish
Jelly fish Humor
Portuguese
Man 0’ War
(a Hydrozoan),
NOT a true
jelly fish
Portuguese Man 0’ War
Tentacles of Physalia physalis
Portuguese Man o’ War
vs. Box Jelly fish
Class Cubozoa: Box Jellyfish
Chironex fleckeri
the Box jelly fish
Phylum Ctenophora
• Contains Comb Jellies
• Characteristics of Ctenophora:
– radial symmetry
– Gastrovascular cavity
– Rows of ciliated bands, called “comb rows”
– No nematocysts; Adhesive structures known
as colloblasts
Comb Jellies