Chapter 26: Sponges,
Cnidarians, Flatworms and
Roundworms
26.1
26.2
26.3
26.4
Sponges
Cnidarians
Flatworms
Roundworms
26.1 Sponges – phylum
Porifera
Asymmetrical
 Invertebrates
 No tissues, organs or organ systems
 Over 5000 species in a variety of sizes,
shapes and colors
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Sponges Are Pore-Bearers
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Porifera = pore bearer
Almost all live in shallow areas of the ocean
Mainly sessile
Sessile - permanently attached to a surface
for all of its adult life
Get food by filter feeding (filter small
particles of food from the water as it pass’s
by or through some part of the organism)
Cell Organization in Sponges
Have different types of cells that
perform different functions
 Sponge embryos do not develop
endoderm or mesoderm, so their cells
are not organized into tissues
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Why Are Sponges Important?
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Can be separated into individual types of cells
but if left alone (over time) the cells will
reorganize back into a sponge
Believed to have evolved from colonial,
flagellated protists
Demonstrate the major evolutionary step
between unicellular life to a division of labor
among groups of organized cells
Reproduction in Sponges
Reproduce both sexually and asexually
 Asexually through fragmentation or
external buds
 Buds may break off and float away to
become new animals or they may
remain attached and form a colony
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Sexual Reproduction in
Sponges
All are hermaphrodites
 Hermaphrodites can produce both eggs
and sperm AT different times
 It increases the likelihood of fertilization
in sessile animals
 Cannot self-fertilize
 Can use either internal or external
fertilization
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Internal Fertilization
Internal fertilization – sperm is
brought into the body and fertilization
takes place inside the organism
 Eggs remain inside the sponge
 Collar cells collect sperm and transfer it
to the amoebocytes
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External Fertilization
External fertilization – sperm and
eggs are released into the water and
fertilization occurs out in the water
 Some sponges in temperate zones
produce gemmules which are like seeds
and lie dormant over the winter and
grow into new sponges in the spring
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Cnidarians (the C is silent)
Activity
Each row will be assigned a cnidarian
that they will become and expert on
 After 5 minutes each expert will share
their information with other experts
until the note sheet is complete
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What are Cnidarians?
Marine invertebrates
 9,000 species
 Jellyfish, corals, sea anemones and
hydras
 Found worldwide, but mainly in warmer
oceans
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Characteristics of Cnidarians
Radial Symmetry
 2 cell layers (from the ectoderm and the
endoderm) with one body opening
 Ectoderm becomes a protective outer layer of
cells
 The endoderm is internal and is adapted
mainly to aid in digestion
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Cnidarians Body Forms
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2 basic body forms that occur at
different stages of their life cycle
Polyp - Tube shaped body and a
mouth surrounded by tentacles
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Dominant in hydras (spends most of its
life in this form)
Corals and sea anemones only have
this stage
Medusa- body shaped like an
umbrella with tentacles hanging down
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Dominant in jellyfish
Body Systems
Have simple nervous systems and other
tissues
 Nerve net – conducts nerve impulses
from all parts of the body
 There is no brain
 Both cell layers have cells that can
contract like muscles
 Simple digestive system
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Digestion in Cnidarians
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Predators that capture or poison their prey
with nematocysts
Nematocyst - capsule that contains a coiled,
thread like tube that may contain a toxin
Digestion involves enzymes and cells adapted
for this purpose
Digestion takes place in the gastrovascular cavity
Undigested materials are ejected back out the
mouth
Nematocysts
Reproduction in Cnidarians
Sexual reproduction usually occurs in
the medusa stage (unless there is
none)
 Asexual may occur in either the polyp
or medusa stage
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**Technically not alternation of
generations like in plants because both
stages are diploid
Common Reproductive Cycle
in Cnidarians
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Male medusae release sperm
Female medusae release eggs
Fertilization occurs
The zygotes develops into an embryo and
then into a larva
The free swimming larva settles down and
develops into a polyp
The polyp reproduces asexually to form male
and female medusae
Respiration
Oxygen enters cells directly
 Because of its body plan, no cell is ever
far from water
 Oxygen dissolved in the water diffused
directly into the cells
 Carbon dioxide and other wastes diffuse
directly out and into the water
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Diversity of Cnidarians
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Most of the 9000 species belong to one
of 3 classes
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Hydrozoans
Scyphozoans
Anthozoans
HYDRA LAB
TAKE OUT HOMEWORK
 READ THE LAB OVER
 CHECK OUT YOUR NEW PARTNERS
 WRITE DOWN SOME SAFETY
PRECAUTIONS
 SIGN YOUR LAB
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Hydras
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Spend lives as polyps (Vase-shaped)
Live in fresh water
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Green hydras live in lakes and streams
Move around by summer salting
Reproduce Asexually – budding
Reproduce Sexually – eggs and sperm
http://cas.bellarmine.edu/tietjen/im
ages/cnidarians.htm
Jellyfish
Jellyfish
 Medusa stage is dominant
 Can be found everywhere in
the oceans and as deep as
1000 meters
 The gastrovascular cavity has 4 internal
divisions
 Range in size from microscopic to more
than a meter
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Jellyfish
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Nematocysts deliver a painful poison
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Located on the tentacles
Can remain active even when broken up
Use these to capture prey
Swimmers nightmare
 The wasp jellyfish produces a strong
nerve poison
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Sea Anemomes
Found in tropical, temperate and
arctic seas
 Cnidarians that exhibit only the polyp form
 All have many divisions in their gastro
vascular cavity
 Sea Anemones live as individual animals
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Sea Anemones
Resemble underwater flowers
 Petals are tentacles
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Petals contain nemocysts
Used to stun and capture prey
Tentacles pull fish into the central
cavity where it is digested.
Clownfish
Mutualistic relationship
 Clownfish serve as bait for other fish
 Anemone keeps the fish safe from prey
 Anemone attacks and digests fish that
are baited by the clownfish
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Corals
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Most form symbiotic relationships with
photosynthetic protists which offer the corals
oxygen and food and use the carbon dioxide
and wastes from the corals
These protists are primarily responsible for
the bright colors of coral reefs
If these protists leave the corals the corals
die
Corals
Soft bodied organisms
 Use minerals to build hard protective
coverings of limestone
 The coverings are left behind when
coral die (Act as a timeline)
 Polyps that live in colonies
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Corals
Mouth surrounded by stinging cells
 Algae live inside coral (Mutualistic)
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Make food for the coral
Perform photosynthesis
Corals found in shallow water
Coral Reefs
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Corals secrete a calcium carbonate ‘skeleton’
that remains after it dies forming
reefs
Reefs grow very slowly
Coral reefs are very sensitive
to
changes in temperature
and water
level
Great Barrier Reef is an
Example
Origins of Cnidarians and
Sponges
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Sponges represent the oldest animal phylum
dating from 700 million years ago
Thought to have evolved directly from
flagellated protists similar to the collar cells of
today
Cnidarians first appear about 630 million
years ago.
We have little evidence for cnidarians as they
are soft bodied and do not fossilize well
Think cnidarians evolved from protists
Videos
http://www.youtube.com/watch?v=12O
mszObAkM
 http://www.youtube.com/watch?v=Ohx
IiV09eMU
 http://www.youtube.com/watch?v=RBd
CpcapB0s
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Reproduction in Planarians
Most are hermaphrodites
 During sexual reproduction individual
flatworms exchange sperm
 Fertilization is internal
 Zygotes (fertilized eggs) are released
into the water to hatch
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Tapeworms (Class Cestoda)
Parasitic
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Made up of a head (scolex) and repeating
sections (proglottids)
The proglottids are detachable and each
contains nerves, muscles, flame cells, as well
as male and female reproductive organs
Each proglottid can have up to
100,000 eggs
A tapeworm can have as many
as 2,000 proglottids
Muscular and Digestive
Systems of Roundworms
Have a pseudocoelom 2 body openings
(mouth and anus)
 Simplest animals with a tubelike
digestive system Have pairs of
lengthwise muscles
 Lack circular muscles
 Move in a thrashing motion
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