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Categorising Animals

Mathematician, computer science expert and animal rights advocate Brian Tomasik estimates the total number of individual animals on the earth to be approximately 20,000,121,091,000,000,000. That is, 20 quintillion, or 20 billion billion! In terms of animal species, while estimated vary widely, there are an estimated 1 to 2 million animal species on Earth.


  1. What is a vertebrate? 
  2. What is an invertebrate? 
  3. What is a Phyla? 
  4. What are examples of Phyla in the animal kingdom?

There are literally millions of species on organisms classified as animals. This means they sit under the kingdom ‘Animalia’. The next level of grouping is called Phylum or Phyla for plural. There are approximately 36 different phyla under the animal kingdom. 

We can also break all animals into two main groups called vertebrates and invertebrates. This is important to know, since asking this question could quickly help you identify an animal. 


Invertebrates have no internal skeleton. They may have their skeleton on the outside (exoskeleton), like a carb and beetles or have no skeleton at all, like a slug. Invertebrates make up more than 96% of all animals on Earth. The following animals below are examples of invertebrates. 

9 main phyla of invertebrates

There are 9 main phyla of invertebrates you should know. These are listed below. Select each image for more information on the characteristics of the organisms in each phyla.




Arthropods have

- Segmented bodies
- Paired and jointed legs
- Exoskeleton
Examples: insects, spiders, centipedes, carbs and crustaceans.




Poriferans have

- spongy body with holes
- found in water
Examples: Sponges.




Cnidarians have

- Soft hollow bodies
- Tentacles
- Live in water
Examples: Jellyfish, corals, anemones and hydra.

Nematodes, Platyhelminthes & Annelida


Nematodes, Platyhelminthes & Annelida are 3 different phyla, but contain similar organisms. Animals in these phyla have:

- Soft, long bodies
- Segmented, flat or round
Examples: Earthworms, leeches, lugworms, Flatworms, flukes and tapeworms.




Echinodermata have

- Rough and spiny skin
- Arms radiating from their centre
- Found in water
Examples: Sea stars, brittle stars, sea urchins, sea cucumbers




Arthropods have

- Soft body
- Sometimes hard protective shells
Examples: Snails, clams, squids, octopi, other mollusks.


Vertebrates have internal skeletons (endoskeleton). Humans, cats, dogs, dolphins, fish and whales are all examples of vertebrates. These animals fit into the phylum Chordata

Phylum Chordata

Chordata contain all the animals that are vertebrates (like you and me). That’s not hard considering 96% of animals are invertebrates. However, Chordata, doesn’t only include vertebrates, it also includes some invertebrates like Sea squirts. 

Sea squirts undergo many physical changes as they become an adult.  One of these is they digest their own cerebral ganglion. This controls their movement and is the equivalent of the human brain. 

Source: https://www.britannica.com/animal/sea-squirt


  • Vertebrates are animals with endoskeletons,

  • Invertebrates are animals with exoskeletons.

  • A Phyla is the next level of grouping after Kingdom. Organisms in a Phyla are similar than those in a Kingdom.

  • Anthropods, Proiferans, Echinodermata, Nematoes and Mollusca are examples of Phyla. These phyla only include invertebrates. 

  • Chordata is a Phylum which contains vertebrates, like you and me. 

Test your knowledge

Click the ‘question mark’ to test your knowledge with some questions and activities.


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