Hydra

Coral

Jellyfish

Sea Anemones

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)

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

Medusas are not attached to any surface. They are

free-swimming creatures. They have tentacles, like

polyps.

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.

Cnidarians capture their prey by releasing nematocysts into their prey. This paralyzes them.

Nematocysts also ward off predators by giving them an irritating sting.

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.

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.

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.

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.

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.

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.

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.

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!

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.

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.

Hydra: Polyp Coral: Polyp Jellyfish: Polyp/ Medusa Sea Anemones: Polyp