1. The Good, The Bad, and the Spineless

2. Invertebrate Characteristics
• They are all very different from each other
• Examples: jellyfish, clams, earthworms,
grasshoppers
• Have 3 different basic body plans, or types
of symmetry
• Can be bilateral, radial, or asymmetry (no
symmetry at all)

3. Bilateral: the two sides of its body
mirror each other.
Radial: Its
body is
organized
around the
center, like
spokes on a
Asymmetrical: cannot wheel
draw a straight line to
divide its body into two or
more equal parts. Its
body is not organized
around a center.

4. Neurons and Ganglia
• All animals except sponges have special tissues
that make fibers called neurons, which allow
animals to sense their environment
• Neurons also carry messages around the body
to control animal’s actions
• Simple invertebrates have neurons arranged into
a nerve cord
• In some, many nerve cells come together as
ganglia

5. • Each ganglion controls different parts of
the body
•Ganglia are controlled by the brain

6. • Gut: pouch lined with cells that release
chemicals that break down food into small
particles
• In complex animals, gut is inside a
coelom
• Coelom: body cavity that surrounds the
gut and contains many organs, such as
the heart and lungs (but kept separate)
• Keeps gut movement from disturbing
other body processes

8. • Sponges cannot move and do not have
gut
• A sponge sweeps water into its body
through its pores
• Water flows into cavity in the middle of the
body, bringing oxygen and food
• Special cells called collar cells line the
cavity and filter and digest food

9. • Water leaves the body
through a hole in the
top of the sponge
called the osculum
• Sponges have
unusual abilities—if
you force it through a
strainer, the parts
come back together
and reform a sponge
—called
regeneration.

10. • A sponge’s skeleton
supports its body and
helps protect it from
predators
• Most sponges have
skeleton made of small,
hard fibers called
spicules
– Some are straight, curved,
or have complex star
shapes
• Sponges are divided into
groups based on kind of
skeleton it has

11. • Cnidarians
– Invertebrates with stinging cells
– Just like sponges, if the body cells are separated,
they can come back together to re-form the cnidarian
– Two body forms
• Medusa: swim through water
• Polyps: usually attach to surface

12. POLYPS
SA
DU
ME

13. • All cnidarians have tentacles
covered with stinging cells
• When an organism brushes
against the tentacles, it
activates hundreds of stinging
cells
• Each stinging cell uses water
pressure to fire a tiny, barbed
spear into the organism
• The tiny spears can release a
painful—and sometimes
paralyzing—poison into their
targets

14. • Cnidarians use their stinging cells to
protect themselves and to catch food

15. 1. Hydrozoans: spend entire
life as polyp
2. Jellyfish: spend of life as
medusas, and catch food
in tentacles
3. Sea anemones and corals:
1. Spend their lives as
polyps
2. Often brightly colored

16. • Simplest worms are
flatworms Flatworms
• All flatworms have
bilateral symmetry
• Many have a clearly
defined head and two
large eyespots (can
sense direction of light)
• Some have bumps on
side of head called
“sensory lobes”, used for
detecting food
• Three major classes:
– Planarians and marine
flatworms
– Flukes
– Tapeworms

17. • Planarians
– Life in freshwater lakes and streams
– Most are predators
– Its head, eyespots, and sensory lobes are
clues that it has a well-developed nervous
system

18. • Flukes
– Parasites
– Most live and
reproduce into
bodies of other
animals
– Flukes have tiny
heads without
eyespots or sensory
lobes
– Have special
suckers and hooks
for attaching to
animals

19. • Tapeworms
– Small head with no
eyespots or sensory
lobes
– Live and reproduce
in other animals
– Feed on these
animals as
parasites
– Tapeworms do not
have a gut—they just
attach to intestines
of another animal
and absorb nutrients

20. Roundworms
• Have long, slim, round bodies
(bilateral symmetry) and a simple
nervous system
• Most species are very small: a
single rotten apple could contain
100,000 roundworms!
• Some break down dead material,
others are parasites
• One roundworm causes the
disease trichinosis