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Sponges and Cnidarians
By: Elina Shapiro and Gilbert
Phylum Porifera (Sponges)
Porifera or sponges are the simplest animal
in the animal kingdom. They have no
tissues, muscles, nerves, or internal
organs. Instead their cells perform actions
that organs are supposed to. There are
5,000 species known to man including the
vase sponge (Ircinia campana), the yellow
sponge (Cleona celata), and the sea squirt
(Didemnum molle).
Vase Sponge
Sea Squirt
Sponges are undoubtedly the first fossils
recovered. They date all the way back to
the Precambrian era.
Symmetry and Body Cavity
Sponges are asymmetrical and acoelomate.
Body Structure
Sponges have three body types: asconoid, syconoid, and
Asconoid- Are tube-shaped and have a central shaft called
the spongocoel.
Syconoid- Similar to asconoids they have a tubular body
but are more complex. These have collar-cell-lined radial
canals that empty into the spongocoel. Water enters
through canals and then filters through tiny holes called
prosopyles into the radial canals. Food is there ingested
by the collar cells. Syconoids usually don’t form colonies
like asconoids do. However, during their development
syconoid sponges do pass through the asconoid stage.
Body Structure Cont.
Leuconoid- These don’t have a spongocoel
and instead have chambers that contain
collar cells. The only way in or out is
through canals.
A sponge skeleton is made up of calcium
carbonate or silicon dioxide that are in the
for of spicules (stiffened rods or spikes
which are also used for defense). Some
don’t even have a skeleton.
Nutrition and Digestion
They feed by filtering food particles
(sometimes bacteria) out of the water
using choanocytes (collar cells).
Choanocytes create the water currents by
beating their flagella. Sponges don’t have
a real digestive system but they do use
choanocytes to digest the food particles.
Transportation and Circulation
While in the larvae stage sponges float
along by means of water currents. As
adults they don’t move at all (they’re
sessil). A sponge has water flow in through
its pores.
Sponges don’t have a respiratory system.
They pump water all through their canals
and extract oxygen from the water.
Water Balance and Excretion
Sponges beat the flagella of certain cells to
pump water in or out. And they don’t have
excretory organs so wastes leaves with
Sponges can reproduce sexually and
Asexually- They reproduce by budding
internally or externally. The new sponges
are exactly like their parent.
Reproduction Cont.
Sexually- Even though sponges are
hermaphroditic they don’t fertilize their
eggs with their own sperm (which would
be asexual reproduction). Instead all the
sponges of the same species release
sperm on one night (usually the full moon)
and fertilize each other in the water. The
new sponges are different from either
Nervous System
Sponges don’t have a nervous system. They
don’t have nerve or sensory cells.
The three classes of sponges are:
Phylum Cnidaria
The Phylum Cnidaria has thousands of living
species worldwide, which include
hydroids, jellyfish [ like the Physalia
physalis (the Portuguese Man of War)],
anemones, and corals.
man of war
Cnidarians were one of the first recognized
animal fossils. They can be dated back
550 million years ago.
The first Cnidarians that were made of soft
tissue only remain today in exceptional
The first coral reefs date back 500 million
years and structurally differ from the ones
Body Structure
Cnidarians can have one of two basic body types:
polypoid or medusoid
Polypoids- have tentacles and a mouths generally
facing up and the other side connected to a
colony of other creatures of the same
species.They also have sturdy skeletons. A
couple of examples of cnidarians with polypoid
body structures would be corals and sea
Body Structure Cont.
Medusoids- this organism is basically
upside-down, with the mouth and tentacles
usually pointed down. These types of
Cnidarians are generally free-swimmers
like jellyfish.
Their endoskeleton is the mesoglea and
their exoskeleton is made up of calcium
carbonate and chitin.
Symmetry and Body Cavity
Cnidarians are radially symmetrical and they
are acoelomate
Most Cnidarians feed on prey that come into
contact with their tentacles. These usually
include large protists, crabs, worms, fish, and
even other cnidarians.
Others like coral live symbiotically with algae
(dinoflagellates and even sometimes chlorophyta). They
absorb the carbon dioxide produced by the Cnidarians,
sunlight via photosynthesis and release oxygen, the
algae produce carbohydrates which the Cnidarians use
as a main food source.
Digestion and Excretion
Since Cnidarians don’t have any organs the
gastrovascular cavity serves as their
stomach and anus. It ingests food and
then secretes digestive enzymes which
break the food down into small particles
that are digested into the cells lining gut.
And the waste is secreted out of where it
came in.
Transportation and Circulation
The nerve net and nerves control the
movement throughout their body. And
Cnidarians have not true circulatory
Cnidarians don’t have a real respiratory
system. Instead respiration takes place
through diffusion of oxygen directly
through their tissues without specialized
organs like the trachea, lungs or even gills.
Water Balance
Cnidarians diffuse water through their tissue.
They can reproduce both sexually and asexually.
Asexual- Asexual larvae bud laterally from adult
polypoid and develop into polypoids themselves.
Budding is usually incomplete so colonies of
identical polypoids tend to form.
Sexually- A key characteristic here is the alteration
of generations. Which is when a asexually
reproducing organism reproduces and has an
organism that can reproduce sexually.
Reproduction Cont.
These grow to full maturity and then release
the male and female gametes. Those then
unite to form a zygote. This forms a
spherical structure (the blastula) through
cell division. The larvae then forms from
the blastula. The larvae then swims until it
finds a surface to attach to. Then it passes
through metamorphasis to the polypoid
Nervous System
Is a nerve net that has a network of nerve
fibers that can communicate when they
The four classes of cnidarians are
Cubozoa (Medusoid)
Scythozoa (Medusoid)
Hydrozoa (Medusoid and Polypoid)
Anthozoa (Polypoid)