Chapter 7 - Cnidarians Animals with stinging tentacles, including:

jellyfish, corals, sea anemones, and hydra

Cnidarians

Cnidarians are soft-bodied animals.

Have stinging tentacles arranged in circles around

their mouth.

May live as single individuals (like anemones) or in

colonies (like coral).

Have radial symmetry

Many cnidarians have a life

cycle that includes two stages: 1. Polyp- a sessile flower-like

stage. 2. Medusa- a mobile bell-

shaped stage.

Cnidarian Anatomy

Two layers of cells.

A saclike digestive tract

with one opening (where

food enters AND waste

exits!)

Tentacles which are long

flexible appendages

arranged in a ring around

a central mouth.

No brain, but they can

respond to stimulus.

Nematocysts – Stinging Cells

Almost all cnidarians

capture their food using

stinging cells called

nematocysts, which

are on their tentacles

Each nematocyst is a

poison-filled sac

containing a coiled

“spring-loaded” dart

When another animal

touches a nematocyst, it

“fires,” paralyzing its prey

Cnidarians do not have a

circulatory system,

excretory system,

nervous system or brain

They have a simple

nervous system, which is

concentrated around the

mouth.

They have eyespots,

which can tell light from

dark.

Cnidarian Anatomy

Most cnidarians can reproduce sexually and asexually.

Asexually- by budding (new organism and detaches from

the parent)

Sexually- by broadcast spawning (sending sperm out

into the water)

Cnidarian Reproduction

Includes 4 groups: jellyfish (1), sea

anemones (2), coral (3) and hydra (4).

3 classes:

1. Scyphozoa

2. Anthozoa

3. Hydrozoa

Phylum Cnidaria

Cnidarians Jellyfish

The Jellyfish Member of the class Scyphozoa.

Umbrella-shaped structure called the medusa, with tentacles hanging down from it.

Epidermis: outer layer

Mesoglea: jelly-like mass separating the membranes.

Gastrodermis: stomach skin.

Jellyfish Movement

Jellyfish are considered

part of the plankton

population; however, they

can move.

Their muscles can

contract the medusa,

causing them to pulsate

through the water.

Respiration in Jellyfish

The membranes of jellyfish are thin: oxygen

diffuses directly from water into the animal’s cells.

How jellyfish obtain food

Cnidoblasts: stinging cells

in tentacles.

These cells can paralyze a

fish with a coiled thread

with a barb at the end

called a nematocyst.

A paralyzed fish can be

taken into the jellyfish by

its contracting tentacles.

How jellyfish obtain food

•Jellyfish can also

catch food using the

medusa.

• The medusa can be

coated in a sticky

mucus that traps

plankton.

• Ciliated cells move

the plankton to the

mouth of the jellyfish.

Jellyfish Reproduction

Adult jellyfish release eggs and sperm into

water (sexual reproduction).

Fertilization = planula larva

Polyp grows on a rock or other surface

(sessile stage).

Polyps clone themselves (asexual

reproduction).

Ephyra are formed.

Adult medusa develops (mobile stage).

Comb Jellyfish

Phylum: Ctenophora

They have 8 rows of long cilia.

They have tentacles for

movement/catching food.

Bioluminescent.

Cnidarians Anemones

Sea Anemones Member of the class Anthozoa.

Anemones have stinging tentacles and a nerve net.

Radial symmetry

They live attached to a substrate with a muscular foot

(sessile).

Sea Anemones: Feeding

Very similar to jellyfish.

They use stinging tentacles to obtain food.

Food is brought to the mouth and digested in

the digestive sac by enzymes.

Sea Anemones: Feeding

http://www.montereybayaquarium.org/videos/Video.as

px?enc=0ZZ+8rD1FkZFMg4UwjaBnQ==

Sea Anemones: Symbiosis

Shrimp and clownfish live among the tentacles:

they have a specialized skin coating that protects them from stings.

clown fish gain protection from anemone.

clown fish protect the anemone’s tentacles from being bitten off by other fish.

Life cycle of anemones

Anemones do NOT have a medusa stage like the

jellyfish.

Polyp stage only (SESSILE).

They can reproduce asexually by splitting in half.

Pieces of a polyps base can break off to make a new

organism.

They can reproduce sexually by broadcast spawning

(releasing sperm into water) – fertilized eggs will settle

and develop into polyps.

http://www.youtube.com/watch?v=Vrq7LEVeDdQ

Cnidarians The Corals

The Corals

Member of the class Anthozoa.

Polyp stage only.

Coral consists of a small polyp that rests within

an expanding bed of limestone.

Grow in the tropics.

Coral are also the home to symbiotic algae

called zooxanthellae.

Symbiosis: Zooxanthellae!

Symbiotic zooxanthellae - a photosynthetic algae that

gives the corals sugars and oxygen .

How does coral grow? Reefs are a massive limestone structure made of calcium carbonate.

To build this structure corals need a source of calcium and carbon.

Polyp cells absorb the calcium from sea water.

Zooxanthellae take up CO2 from coral respiration.

Coral Colonies

Coral polyps live in large

groups and are attached to

one another by a thin

membrane.

Membranes connect the

coral digestive systems so

that there is sharing of food

between polyps.

TED Talk Lesson

“Conserving our spectacular, vulnerable coral

reefs” - Joshua Drew

Go to this link: http://ed.ted.com/on/rHi5crC4

Cnidarians Hydroids

Hydroids

In the class Hydrozoa.

Colonial animals: made up of

individual polyps that function

together.

Two types of polyps:

1. Feeding polyps (have

nematocysts)

2. Reproductive polyps

(have a brief medusa

phase)

Portuguese man of war:

This organism is classified

with hydrozoans and not

jellyfish because it is a

colony made up of different

types of polyps.

Like the rest of the

cnidarians it has many

nematocysts on its

tentacles.

Physalia – Different types of

polyps

A gas filled bag keeps the

colony afloat – one polyp

type.

Colony of stinging tentacles

– another type of polyp.

Some polyps serve a

reproductive function.

Hydroid Reproduction

Dominant phase is a polyp.

They can reproduce sexually with a brief

medusa (free swimming sexual phase).

Can also reproduce asexually through budding.

http://www.youtube.com/watch?v=wfbhwq95Duc