1. Chapter 2, Lesson 1 What are invertebrates?
Animals have many things in common. They also have many things that are different. These features can be used to classify animals.

2. Symmetry
Animals have different body shapes. Most animals have symmetry. Symmetry means that parts of an animal’s body match up. The body parts match up around a midpoint or line. Some animals have no symmetry. We can use symmetry to classify animals.
Sea urchins have symmetry.
Sponge does NOT have symmetry.

3. Backbone or No Backbone
Some animals have a backbone and others do not. A vertebrate is an animal that has a backbone. An animal without a backbone is an invertebrate.
Most animals are invertebrates. Some invertebrates have a hard outer covering. Others have a skeleton inside their bodies.

4. Invertebrate Groups Mollusks Cnidarians Sponges Echinoderms Flatworms
Roundworms
Segmented worms
Arthropods

5. Sponge facts Simplest kind of invertebrate
Most are shaped like a sack with an opening at the top
Live under water
Example: sponge

6. Cnidarians Have arm-like parts called tentacles
Stinging cells at the end of each tentacle
Stun prey
Some stay in one place
Others float or swim
Examples: corals, jellyfish

7. Mollusks Have a shell Some have shells inside the body
Most live in water
Some swim
Others stay in one place
Snails and slugs are the only mollusks that live on land
Examples: clams, oysters, octopuses, squid, and snails

8. Echinoderms Spiny skin
Have a support structure inside the body called an endoskeleton (means inside the body)
Example: sea urchin

9. Quick Check What are two ways we can classify animals?
All mollusks live in water. _________
A sponge is the simplest kind of invertebrate. __________
An echinoderm has soft skin. _________
Cnidarians have tentacles. ___________

10. What are arthropods?
The largest group of invertebrates is the arthropod group.
Arthropods have legs that bend. Their bodies have sections.
Some breathe with gills and others through tubes.
Every arthropod has an exoskeleton. This is a hard covering on the outside of the body.

11. Exoskeleton Keeps the animal safe Keeps the animal from drying out.
Quick Check
An arthropod has a(n) ________ covering.
The covering is on the ________ of the body.
Examples: lady beetle, praying mantis, moth

12. More examples of arthropods
Insects- have one pair of antennae, three pairs of legs, one or two pairs of wings, and three body sections.
Arachnids- include spiders, ticks, and scorpions. They have four pairs of legs, two body sections, and fangs.

13. Examples Continued
Crustaceans- such as crabs and shrimps, have two pairs of antennae and two to three body sections. They can chew
Centipedes and millipedes- Centipedes have one pair of legs on each body section. Millipedes have two pairs of legs on each body section.

14. How are worms classified?
There are 3 kinds of worms: flatworms, roundworms, and segmented worms.

15. Flatworms Simplest worms Flat bodies They have a head and a tail
Most do not hurt other living things
Some live inside other animals.

16. Roundworms They have thin bodies with pointed ends.
Not as thin as flatworms
Food comes into opening
Waste leaves through another opening.
Most live inside other animals.

17. Segmented Worms Bodies are divided into parts, or segments.
The parts are the same, except for the head and tail ends.
Each has an opening for the digestive system.
Most live on land
They do NOT live inside other animals.
Earthworms, sandworms, and leeches are segmented worms.

18. Quick Check Write the letter for the fact about each worm.
______flatworms
______ segmented worms
______ roundworms
A. thin bodies with pointed ends
B. do not live in other animals
C. simplest kind of worms