Cnidarians
Jellyfish, Corals Anemones
and Hydroids
Cnidarians eat mussels,
fish, plankton, and worms.
Cnidarians eat by
stinging their prey so it
becomes paralyzed,
and then they bring the
food into their
stomach.
Phylum Cnidaria
1.
2.
3.
4.
5.
6.
7.
Soft bodied animals with stinging tentacles
arranged in circles around the mouth
Radial Symmetry
Specialized cells and tissues, including nervous sys
Lifecycles often include two different stages:
polyp and medusa
3 Body layers: Ectoderm, Mesoderm, Endoderm
Nematocysts – stingers
Only one internal cavity, the digestive cavity, with a
mouth, but no anus.
Life Cycle & Polymorphism
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Two basic types
of individuals:
polyps and
medusae.
Dominance of
Medusa or Polyp
lifecycle varies
species to
species.
Polyp Stage of Life Cycle
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Polyp = adapted
for sedentary or
sessile life.
Tubular body w/
mouth at one
end surrounded
by tentacles.
May live singly or
in colonies.
Colonial polyps
Medusa

Medusa = jellyfish form, free swimming and sexually
mature form,
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bell-shaped or umbrella-shaped bodies,
radial symmetry
mouth centered on concave side, tentacles and one or more
types of sense organs borne on rim of umbrella.
Medusa provides dispersal mechanism so don't
compete with parents. Mesoglea much thicker than in
polyp - constitutes bulk of animal - makes it buoyant
= "jelly" of jellyfish.
Medusa
CNIDARIANS have no
bones, are hollow with 3
layers of cells.
They live in salt or fresh
water.
When a cnidarian
reproduces, the young hatch
into the mother stomach,
then, She spits them out.
Classification of Cnidarians
Classes: Scyphozoa, Cubozoa and
Anthozoa
1.
2.
Jellyfishes (Classes Scyphozoa and Cubozoa)
are predominantly medusae w/ polyp stage
very reduced or completely absent.
Corals and anemones (Class Anthozoa) are
entirely polyps, no medusa.
The Portuguese Man o War
wasn’t just a Ship
Physalia from Jamaica
Portugues
e Man O
War
A tenacious
hunter with a
taste for fish
and the
poison to
render most
prey helpless
Yikes!
Portuguese Man 'O War
Physalia physalia
Size: to 1 ft (float) and 50 ft (tentacles)
Habitat: floats at the surface
Notes: dangerous
Fortunately, this creature, with its powerful battery of stinging
tentacles, is more common in bays and protected waters than in the
open ocean. The sting of the Man'O'War can vary from extremely
painful to incapacitating to fatal, depending on the severity and the
victim's reaction.
Jellyfish sting to defend themselves.
The Man of War is poisonous to humans.
When a cnidarian
reproduces, the
young hatch into
the mother’s
stomach, then, she
spits them out
Other Dangerous Jellyfish
Moon Jellyfish / Red Jellyfish ( Lion's Mane )
Aurelia aurita / Cyanea capillata
anywhere
Notes:
Jellyfishes are free-swimming relatives of corals,
anemones, and hydroids. In fact, in many cases they are
the same animal, just in a different stage of life ! Not all
medusas ( as jellyfishes are called ) have a
corresponding polyp stage, and likewise not all polyps
have a corresponding medusa stage, but most conform
to this life cycle. Small jellies ( up to 1" across ) are most
likely the medusa stage of some hydroid, while large
jellies are usually the dominant stage of a species in
which the polyp stage is almost absent.
Translucent Moon Jellies are harmless and quite
common. Red Jellies have a painful wasp-like sting, but
are usually much less common. And try as you might to
avoid it, sooner or later every northern diver will get a
stray tentacle draped across the face and lips - the only
places exposed to attack.
Habitat:
Moon Jellyfish
Beached Moon Jellies: the surf has stripped away all the tentacles,
leaving just a harmless dying blob of goo.
Red or
Lion's Mane
Jelly
Avoid these.
Swim away
– swim away
NOW! !
Nematocysts
1. Hold prey
2. Sticky -- aid in locomotion by attaching tentacles
3. Penetrate and anchor in prey and poison it.
Nematocysts can be Pretty
Nematocyst poison
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Most dangerous to man is Cubozoan jellyfish, the sea
wasp (Chironex fleckeri). Caused more human
suffering and death off Australian coasts than
Physalia (Portuguese man-of-war) has in any of its
home waters.
Symptoms range from:
1.
2.
3.
4.
5.
burning pain at site of contact
lesions and eruptions of various sorts, often severe
enough to leave scars,
great pain, fever, and respiratory interference.
severe reactions due to shock & allergies
"Sting" of most is imperceptible to humans.
Problems usually occur only when repeatedly stung.
Clown fish live in
anemones, and coral
and they’re immune to
stings!
Fire Coral and Tube Anemone
Reproductive Characteristics
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Asexual reproduction by budding (in polyps)
Sexual reproduction by gametes (in all
medusae and some polyps).
Sexual forms monoecious or dioecious;
primitive gonads; ciliated free-swimming larva
in life cycle of most