Lesson 8
Classifying Animals
SC PASS Coach - Science
Classifying Animals
You learned in Lesson 7 that scientists classify plants into two big groups. Scientists sort
animals into two big groups, too. Then scientists sort those big groups into smaller groups.
Two Main Animal Groups
As you have learned, all animals have one important thing in common. Unlike plants, animals
cannot make their own food. All animals get energy from eating plants or other animals.
Scientists classify animals into two main groups – those with backbones and those without
backbones. A backbone is a row of connected bones down the middle of the back. These
bones are called vertebrae. Vertebrates are animals that have backbones. Animals without
backbones are called invertebrates. You are a vertebrate. So is a snake. An earthworm is an
invertebrate.
Vertebrates
Besides backbones, vertebrates share other physical features. Vertebrates have a covering of
skin that protects them. They have a framework of bones called a skeleton inside their bodies.
Muscles help these animals move. They have blood that moves through tubes called blood
vessels. And vertebrates have lungs or gills for breathing.
Scientists sort vertebrates into five smaller groups. These groups are shown below, with an
example of each.
Vertebrates
Fish
Amphibians
Reptiles
Birds
Mammals
Fish are vertebrates that live in water. They breathe with gills. Most fish have scales on their
bodies and fins that help them swim through the water. Most fish lay eggs in water, and their
young grow from the eggs. Some examples of fish are perch, tuna, trout, and carp.
Amphibians spend the first part of their lives in water. They breathe underwater with gills, like
fish. Then they change form and develop lungs. As adults, they breathe air and can live on
land. They have smooth, moist skin. Most amphibians lay eggs. Frogs, toads, newts, and
salamanders are amphibians.
Reptiles breathe air using lungs. Reptiles have scales or plates on their skin. Most lay eggs on
land. Snakes, lizards, turtles, alligators, and crocodiles are reptiles.
Page 1 of 3
Lesson 8
Classifying Animals
SC PASS Coach - Science
Fish, amphibians, and reptiles have body temperatures that change with their surroundings..
When the water or air gets cooler, their bodies cool off, too. Snakes, lizards, and other reptiles
lie in sunlight to warm up. They move into the shade to cool off.
Birds have feathers covering their skin. They have a beak, two feet, and two wings. Birds live
on land, breathe with lungs, and lay eggs. Most fly through the air to get from place to place.
Unlike fish, amphibians, and reptiles, birds keep a constant body temperature. Their bodies
stay warm even when the air around them cools off.
Mammals are vertebrates that have hair or fur. They breathe using lungs. The young of almost
all mammals grow inside the mother until they are ready to be born. Once mammal babies are
born, they are fed milk from their mother. Like birds, mammals keep a constant body
temperature. Whales, bears, cats, dogs, and humans are a few kinds of mammals.
Invertebrates
About 95 percent of all animals are invertebrates. They do not have backbones. Some
examples are spiders, lobsters, sponges, sea stars, and snails.
Some invertebrates have a hard covering or shell on the outside of their bodies. These animals
include insects, spiders, crabs, snails, clams, and others. Other invertebrates, such as squid,
jellyfish, and earthworms, do not have a hard covering.
Invertebrates
Sea Urchin
Grasshopper
Scorpion
Squid
DISCUSSION QUESTION
What kind of organism is a fox? Explain your answer.
Why do you think the first way an animal is classified is by whether it is a vertebrate or an
invertebrate?
Page 2 of 3
Lesson 8
Classifying Animals
SC PASS Coach - Science
LESSON REVIEW
1. Which of these animals is a vertebrate?
a. spider
b. snail
c. worm
d. cat
2. Some but not all invertebrates
a. have backbones.
b. have shells.
c. have no backbone.
d. can make their own food.
Resource:
Schuster, Janette (2010). Classifying Animals. South Carolina PASS Coach: Science 4, 46-49.
Page 3 of 3