Cnidarians like hydra, jellyfish, coral, and sea anemones can take the form of polyps or medusas. Polyps are attached to surfaces while medusas are free-swimming. They capture prey using nematocysts in their tentacles and digest food in their guts. Reproduction varies between species, but includes both asexual budding and sexual reproduction.

2.  Hydra
 Coral
 Jellyfish
 Sea Anemones

3.  Cnidarians can take different forms.
 They can take the form of a polyp (i.e. sea
anemones, hydra and coral)
 They can also take the form of a medusa (i.e.
jellyfish)

4. Polyps
 Polyps are anchored down onto a surface with a
mouth and tentacles on top and a basal disk on the
bottom. (This is why they are commonly mistaken
for plants.)
Sea Anemone Hydra Coral

5.  Medusas are not attached to any surface. They are
free-swimming creatures. They have tentacles, like
polyps.

6.  All cnidarians have radial symmetry, which
means that they can be cut into two
identical halves by any longitudinal cut
through their center.
 Cnidarians have no excretory or respiratory
systems, because their thin epithelial layers
allow for them to release and take in the
things they need.
 Cnidarians reproduce sexually and asexually.

7.  Cnidarians capture their prey by releasing nematocysts
into their prey. This paralyzes them.
 Nematocysts also ward off predators by giving them an
irritating sting.

8.  After the nematocysts paralyze the prey,
the cnidarian proceeds to digest it in its gut.
 When it has been digested for a while, the
prey is pulled into the inner cells, where the
digestion process is completed.

9. HYDRA
One form of cnidarian is a hydra. A hydra
has tentacles and a mouth at
one end and is anchored by a
basal disk at the other. This
means that it is a polyp.

10. Hydra Reproduction
 Hydra reproduce asexually and sexually.
 Hydra reproduce asexually by
budding. A small lump forms on the hydra
And grows tentacles. It slowly breaks free
from the original hydra, and a new hydra
is formed.
 Hydra can be hermaphroditic, which means
that they have male and female reproductive
organs. They can have both ovaries and
testes, and can release both eggs and sperm into
their surroundings. When these come into contact
with each other, a new hydra is formed.

11. Coral
 Another form of cnidarian is coral. Coral
are in polyp form. They attach themselves
to stones and then can form huge coral
reefs when one coral dies and more corals
attach themselves to the dead ones.

12.  Coral is actually colorless. Coral provides a home
to many algae, and these give them their wild
colors.
 The algae that live on the coral are
photosynthetic, and they provide food for the
coral.
 Coral takes up less than 1% of the ocean floor (or
the area of France) but are essential for 25% of
the creatures in the ocean.

13.  Another form of cnidarian is jellyfish. Jellyfish
spend part of their life as a polyp and part of their
life as a medusa.
 Jellyfish reproduce asexually (via budding) in their
polyp form and sexually in their medusa stage.
 Jellyfish in their medusa stage are either male or
female. They can’t be hermaphroditic, like hydra.

14. Jellyfish Reproduction
 Sperm is released into the water
and goes into the gut of a
female. This produces a
fertilized egg which grows into a
larva. This grows into a polyp
and the polyp transforms into a
medusa. This then grows into
an adult medusa and the
process begins over again.

15.  Jellyfish have no blood or brain!
 Jellyfish can be transparent; this is because they
are 90% water!
 The largest recorded jellyfish was 7 feet, 6
inches across the top, and its tentacles were 120
feet long. They can be as small as a thimble!
 Millions of people live in areas which jellyfish
inhabit. 200,000 people are stung in Florida
annually!

16.  The fourth form of cnidarian is the sea anemone. Sea
anemones are in polyp form.
 Sea anemones’ nematocysts are chemically triggered.
 Sea anemones can reproduce asexually or sexually.
They can be hermaphroditic (containing male and
female reproductive organs) but they can also
reproduce asexually via budding.

17.  Sea Anemones have two major symbiotic
relationships. These are relationships in
which one of the two (or +) species
benefits.
 The sea anemone has a symbiotic
relationship with algae. It hosts them, and
it gets the byproducts of their
photosynthesis.
 The sea anemone also has a symbiotic
relationship with clownfish. The clownfish
have a mucus covering which makes it so
that they are not stung by the anemone’s
nematocysts. They get a home, safe from
predators. The clownfish attracts food for
the anemone.

18.  Hydra: Polyp
 Coral: Polyp
 Jellyfish: Polyp/ Medusa
 Sea Anemones: Polyp