23.3 Sponges and Cnidarians
KEY CONCEPT
Sponges and cnidarians are the simplest animals.
23.3 Sponges and Cnidarians
Sponges have specialized cells but no tissues.
• Sponges are the most primitive
animals on Earth.
– 570 million-year-old fossils
– closely related to group of
protists
• Sponges share common
characteristics.
1. Sessile adult, motile larvae
2. reproduce both sexually
and asexually
3. filter feeders
4. No tissues or symmetry
23.3 Sponges and Cnidarians
•
1.
2.
3.
Sponges have several types of specialized cells.
Pinacocytes- outer layers
Choanocytes- filter feeding mechanism
spicule
amoebocytes -motile
pore
osculum
pinacocyte
amoebocyte
choanocyte
23.3 Sponges and Cnidarians
Cnidarians are the oldest existing animals that have
specialized tissues.
• Cnidarians have two body forms.
1. polyps
In the polyp
form
of a coral, the
tentacles
and mouth
face upward.
23.3 Sponges and Cnidarians
2. medusas
In the medusa form of a
sea jelly, the tentacles
and
mouth face downward.
23.3 Sponges and Cnidarians
• Cnidarians are made up of two
tissue layers (endoderm and
ectoderm) separated by mesoglea.
• The outer tissue layer has three
cell types.
1. contracting cells
2. nerve cells
3. cnidocytes (which contain
nematocysts to ) discharged
nematocyst
barbs
coiled
nematocyst
gastrovascular cavity
mouth
mesoglea
tentacle
oral arms
23.3 Sponges and Cnidarians
Two anemones aggressively fight using their
specialized sacs loaded with nematocysts that
contain toxins.
http://shapeoflife.org/video/cnidariansanemones-fight
23.3 Sponges and Cnidarians
• The four major cnidarian classes are defined by their
dominant body form.
– Anthozoans such as sea anemones have a dominant
polyp stage.
23.3 Sponges and Cnidarians
– Hydrozoans such as hydra alternate between forms.
23.3 Sponges and Cnidarians
– Scyphozoans are true
jellyfish with a dominant
medusa form.
– Cubozoans such as sea
wasps have a dominant
medusa form.
23.3 Sponges and Cnidarians
Sponges and Cnidarians Virtual Lab
Link:
http://www.glencoe.com/sites/common_assets/science/virtual_l
abs/LS13/LS13.html