Download Chapter 7 - Cnidarians

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 bellshaped 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
Cnidarian Anatomy
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 Reproduction
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)
Phylum Cnidaria
Includes 4 groups: jellyfish (1), sea
anemones (2), coral (3) and hydra (4).
3 classes:
1. Scyphozoa
2. Anthozoa
3. Hydrozoa
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