Download 2. Coelenterates

2. Coelenterates
(phylum Coelenterata)
The word
coelenterate means
“hollow body cavity”.
All coelenterates
contain a central
cavity with only one
opening .
There are two general
body forms found
among the
coelenterates.
POLYP
MEDUSA
The Polyp form is
usually sessile and has
a cylindrical body with
a mouth and tentacles
at the upper free end.
Corals and Hydras are examples
Characteristics of coelenterates ;
- The members of this
group are
jellyfish,
sea anemones, corals
and polyps .
- The habitat of
coelenterates is salt
water but some of them
live in fresh water.
- They do not have a
complete nervous
system but they have
nerve net .
- Coelenterates have
a sac like gut which
serves as mouth and
is surrounded by
tentacles.
- Their respiration
method is similar to
that of sponges. They
respire only by means
of diffusion across the
cell membrane.
- Although most
coelenterates reproduce
sexually, some of them
reproduce by budding
- Coelenterates have
two definite tissue
layers; an ectoderm
and an endoderm.
The structure of a hydra
is a typical example of a
coelenterate.
It consists of a body
wall within which is the
gastro vascular cavity.
A group of tentacles
surrounds the mouth
that opens into the
cavity.
The body wall of
coelenterates has an
outer layer (ectoderm),
an inner layer
(endoderm) and
an intermediate
layer, the mesoglia.
The intermediate
layer contains cells
and jelly like
substances.
The gastro vascular
cavity serves both as
a circulatory and
digestive system.
It is surrounded by
an inner layer of the
body that is made up
of secretory cells and
columnar cells.
These cells have the
ability to engulf food
particles. They are
digested and then
diffuse form the
body.
SUMMARY
Coelenterates
- Coelenterates have
a central body cavity
with one opening.
-Most Coelenterates have
stinging cells called
nematocysts on their
tentacles.
Coelenterates sting
and capture their prey,
which they digest in the
central body cavity.
Waste products are
released through the
mouth.
Coelenterates (Phylum Coelenterata)
1. Digestive cavity
2. Two life stages:
attached polyps and
free-swimming medusa
3. Tentacles with
stinging cells
4. Radial symmetry
5. Nerve net
6. Aquatic organisms
Hydra
The hydra is a simple
multicellular animal about 5
millimeters long from the tip of
its tentacles to its base.
The body of the hydra is a
hollow cylinder made up of
two layers of cells.
1. The outer layer is the
ectoderm . The ectoderm is
in direct contact with the
aquatic environment
2. The inner layer is the
endoderm. The endoderm
lines the gastro vascular cavity.
Hydra is in contact with
water because water
freely enters and leaves
the gastro vascular cavity
through the mouth
endoderm
tentacles
ectoderm
cnidoblast
nematocytes
The hydra captures its food
with its tentacles.
When a water flow or some
other small animal comes in
contact with a tentacle, the
discharge their long threads.
Some of the threads wind
around the prey, nematocysts
while others inject a poison
that paralyzes the animal.
By movements of the tentacles,
the food is stuffed through the
mouth and into the gastro
vascular cavity , where digestion
begins
CORAL
CORAL
Corals
Corals are small
polyp that grow
in colonies.
Unlike hydras,
they are
surrounded by a
hard skeleton
Corals, like all
coelenterates, are softbody organisms.but corals
use minerals in the water
to build a hard protective
covering of limestone.
Corals
When the
coral dies,
the hard
outer
covering is
left behind.
Coral
• The mouth of
this coral is
surrounded by
tentacles.
• What is the
function of
tentacles?
Algae live inside the coral`s body.
The algae help make food for
the coral.
Since algae need sunlight to
make food , corals must live
in shallow water where
sunlight can reach them.
This relationship between a
coral animal and alga plant is
among the most unusual in
nature
Coral, like all
coelenterates, are
soft-bodied
organisms. But coral
use minerals in the
water to build a hard
protective covering of
limestone.When the
coral dies, the hard
outer covering is left
behind.
Sea Anemones
Sea anemones look like
underwater flowers.
However, the “petals”
are really tentacles, and
their brilliant coloring
helps attract passing fish.
When a fish passes over the
anemone`s stinging cells,the
cells poison the fish.
The tentacles then pull the
fish into the anemone`s
mouth, and the stunned prey
soon is digested.
The clownfish, however, is
not harmed by the
anemone.It is not affected
by the anemone`s poison
and swims safely through
the anemone`s tentacles
In this way, the
clownfish is protected
from other fish that
might try to attack it.
At the same time, the
clownfish serve as a kind
of living bait for the
anemone. Other fish see
the clownfish, come closer,
and are trapped by the
anemone.
Jellyfish
Jellyfish
If you saw a jellylike cup
floating in the water,
recognize this coelenterate,
the jellyfish.
Although the jellyfish may
look harmless, it can deliver
a painful poison through its
stinging cells.
In fact, even when they are
broken up into small
pieces, the stinging cells
remain active and can sting
a passing swimmer who
accidentally bumps into
them.
Like the
other
coelenterates
, jellyfish use
the stinging
cells to
capture prey
Aurelia is a common
jellyfish. Its life cycle
includes both medusa and
polyp forms.The jellylike
body of the medusa is the
form commonly seen on
beaches.
Protective tentacles
hang from the edge
of the umbrella-like
body
The sexes are separate
in Aurelia, but the male
and female look alike.
Sperm from the male
medusa are released into the
surrounding water.
Some sperm cells enter
the gastro vascular
cavity of a female
medusa, where
fertilization occurs.
Early development
occurs while the zygote
is attached to the female.
The zygote develops into
a small, oval-shaped,
ciliated larva called a
planula.
The planula is free
swimming for some
time.It then becomes
attached by one end to a
rock.
The larva develops a
mouth and tentacles at
the unattached end and
becomes a polyp.
The polyp grows,
eventually reproducing
asexually to form
medusa.This occurs in
the fall and winter.
The Reproductive Stages
The medusa stage reproduces
sexually by the production of
egg and sperm, and it gives
rise to the polyp stage.
The polyp stage reproduces
asexually by budding and give
rise to the medusa stage.
1.Asexual Reproduction
2.Sexual reproduction
Both type of reproduction,
occur in the life cycle of
any living things is called
Alternation of generation
Worms