Animals Without Backbones Chapter 2: The Animal Kingdom

Scientists keep track of Earth’s animal species by observing their similarities and differences.

An animal with symmetry has body parts that match other body parts around a midpoint or line.

Animals can be classified by whether or not they have a backbone.

More than 95 out of every 100 animals are invertebrates.

The simplest invertebrates are sponges.

The shape of a sponge does not have symmetry.

Invertebrates that have stinging cells on their tentacles are called cnidarians.

Clams, squid, and snails are soft-bodied invertebrates with hard shells and are called mollusks.

Sea stars, sea urchins, and sand dollars are spiny- skinned invertebrates, called echinoderms.

All echinoderms have a support structure inside their bodies, called a(n) endoskeleton.

Invertebrates with jointed legs and body sections are called arthropods.

Arthropods have a hard outer covering, called a(n) exoskeleton, that protects their bodies and holds in moisture.

Worms are classified as flatworms, roundworms, or segmented worms.

Flatworms have ribbon-like bodies, and some types live inside the bodies of other animals.

Roundworms have thin bodies with pointed ends.

Exit Question In the margin of your paper, answer the following questions: If you were an animal, what would you be and why? Would your animal be considered a vertebrate or invertebrate?