Animal Classification

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A series of free Science Lessons for 7th Grade and 8th Grade, KS3 and Checkpoint Science in preparation for GCSE and IGCSE Science.

Animal Classification - Vertebrates
Animals are classified into different groups based on their characteristics. Invertebrates are animals that do not have a spine, or backbone. Vertebrates are animals that do. Vertebrates are further classified into fish, amphibians, reptiles, birds, and mammals.

Invertebrate Animals
Animals are divided into two big groups, the vertebrates that have an internal skeleton formed by bones and the invertebrates that have no bones.
Some examples of invertebrates are:
Sponges, jellyfish, corals, worms, mollusks, echinoderms and arthropods.

The sponges are aquatic animals, that are sac shaped and their body is full of pores.

The jellyfish live in the ocean. Their bodies are gelatinous and have tentacles. Their tentacles have small venomous stingers that produce very unpleasant bites.

Corals are tiny marine animals that produce limestone residue, which give rise to beautiful shapes.

Worms are soft and long invertebrate animals that move by dragging their body in the ground, because they have no feet. They can be aquatic or terrestrial.

Mollusks have a soft body, without legs and can also be aquatic or terrestrial. Some, like snails, clams and mussels, protect their soft body with shells, but there are other mollusks that don’t have a shell to protect themselves like slugs or octopuses.

The echinoderms are exclusively aquatic animals. Their bodies have calcareous plates that form a shell. Some echinoderms are balloon shaped and are covered in spikes that they use to defend themselves, like sea urchins. Others are star shaped, and called starfish.

The arthropods are the most abundant animals on the earth. Of every 100 animals that exist, 80 are arthropods. These invertebrate animals have their body covered by an external skeleton called a cuticle. The most common way to classify the arthropods is by the number of legs they have. This way we can classify them in four big groups.

Arthropods with 6 legs. Insects, like ants and flies.
Arthropods with 8 legs. Arachnids, like spiders and scorpions.
Arthropods with 10 legs. Crustaceans, like crabs and lobster.
Arthropods with more than 10 legs. Myriapods, like centipedes.

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