Classification of Animals

In order to study living things better, we classify (arrange) them into a series of groups according to the features they share.

Types of Skeleton

We can classify animals according to their skeletons. Animals can be broadly divided into two groups: invertebrates and vertebrates.

Invertebrates are animals that do not have a backbone. Invertebrates can come in many shapes and sizes. Many live in the sea (crabs, lobsters and octopus). This group also includes include insects and spiders, slugs, snails and worms. 97% of all animals are invertebrates!

Vertebrates are animals with a backbone. This group includes reptiles, fish, amphibians, birds and mammals. The flexible internal skeleton allow them to grow much larger than more invertebrates and yet move around easily.

Another way to classify is by the type of skeleton

  • An endoskeleton (endo = inside) is an internal skeleton, such as bones within the body.

  • An exoskeleton (exo = outside) is an external skeleton, such as a shell outside the body.

A hydrostatic skeleton (hydro = water) provides support with water pressure. Hydrostatic skeletons work like a rubber glove filled with water and sealed at the wrist — the water forces the fingers of the glove to stand up.

Types of Vertebrates:

Mammals:

  • warm blooded (heat is made inside their body, which keeps them warm

  • most mammals have a coat or hairs (other mammals like dolphins spend all their time in the water so do not need a furry coat- instead they have a thick layer of fat)

  • all baby mammals are nourished by milk- made by their mothers and so are dependent on their mothers for the early years.


Reptiles

  • Reptiles are cold-blooded, which means that they rely on heat from their surroundings.

  • They have dry skin, covered with either scales or horny plates.

  • Most reptiles eat other animals

  • Most lay eggs on land to breed

Amphibians

  • Amphibians are cold-blooded, which means that their body temperature changes with their surroundings.

  • They spend part of their lives in water (breathing with gills) and part of their lives on land (breathing with lungs)

  • They have smooth, moist skin

  • Most lay eggs

Birds

  • Birds have wings and feathers

  • Most can fly, using powerful muscles

  • Birds' bodies are covered with a light, tough layer of feathers and have very light skeletons.

  • Instead of teeth they have beaks.

  • Birds hatch from eggs and many species build nests where their eggs can develop in safety,

Fish

  • A fish is cold blooded vertebrate.

  • It has scaly skin and swims in water, using gills to breathe.

  • Sharks and rays skeletons are made of a much softer substance called cartilage.

  • A fish flaps a tail to swim and uses fins to stay upright and steer.

  • A fish lays eggs to reproduce.