Unit 3: Animals

Vertebrates and Invertebrates


There are two groups of animals: vertebrates and invertebrates.


Vertebrates have a backbone or internal skeleton.


Invertebrates do not have a backbone or internal skeleton.





Invertebrate animals do not have a backbone. Some of them have an external skeleton or shell that protects their body. Most invertebrates are smaller than vertebrates.



Insects are invertebrates. Insects are the largest group of animals in the Earth. Flies, butterflies, ants and ladybirds are insects. Insects have six legs. Some of them can fly.



Arachnids are invertebrates. Spiders and scorpions are arachnids. Arachnids have eight legs. They can't fly.



Mini online invertebrate encyclopedia




Online invertebrate quiz





The Life Cycle of a Butterfly



A butterfly lays its eggs on a leaf.


A caterpillar or larva hatches from an egg. The caterpillar is always hungry and eats a lot.


The caterpillar grows and forms a hard shell called a pupa. The butterfly forms inside the pupa.


When the insect comes out, it is a beautiful adult butterfly. It has wings and legs.




Vertebrate animals have a backbone and a skeleton. We can classify vertbrates into five groups: fish, amphibians, reptiles, birds and mammals.





Salmon, clownfish and sharks are fish. Scales cover their bodies. Fish don't have legs. The have fins. They breathe through their gills.





Snakes, lizards, turtles and crocodiles are reptiles. Thick scales cover their bodies. Some reptiles, like snakes, don't have legs.





Frogs and newts are amphibians. Scales don't cover their bodies. Their skin is moist and smooth. Most amphibians have four legs.





Parrots, eagles, and penguins are birds. They have wings and a beak. Feathers cover their bodies. Most birds can fly.




Lions, whales, bats and horses are mammals. Hair or fur covers their bodies. They have lips. When they are babies, their mothers feed them with milk from their bodies.



Life Cycle of a Mammal



Most mammal embryos grow inside their mother's bodies.


When the babies are born, the mother feeds them with her milk.


Young mammals spend time with their parents. They play and learn the skills they need to survive.


When they are adults, they become mothers or fathers too!