Invertebrates: The Spineless Wonders Of Our World

Most animals – in terms of either the numbers of individuals or the number of species – are invertebrates.

Of the 34 phyla of animals in the Kingdom Animalia, 32.5 of them are invertebrates…

That is, they are lacking a spine or vertebra (you know, that collection of bones that runs along the back of animals like fish, frogs, snakes, birds and mammals)

Life evolved in water…

And the greater proportion of it has stayed there. Mostly in the sea, but some also in fresh water.

Of the 34 phyla of animals, 25 are exclusively aquatic and 19 exclusively marine. Of the 8 phyla that have some terrestrial living members, only two are predominately terrestrial: Chordata (including the Vertebrata) and Arthropoda (including the Insecta).

This – and the fact that 20 of the phyla contain less than 500 species – explains why we often remain completely unaware of this wonderful diversity of life that shares our planet with us.

invertebrate mantis shrimp Stomatopoda
Mantis shrimp of order Stomatopoda

These invertebrates with their huge numbers – but often invisible lives – keep the planet healthy.

They are part of the great tapestry of life… and like the stitches that hold your clothes together, they are essential to our existence.

“Without them our lives would not be possible.”

To understand our own lives and our place in this world fully, we need to appreciate something of this diversity and the role it plays in maintaining the environment we live in.

The invertebrates as a whole are a fascinating group of animals. Many are very beautiful and of great scientific interest – helping us gain important insights into how the world works.

Others are of great economic importance, both to our ancestors and to ourselves in our busy technological lives. They feed us, both directly and indirectly, and clean up the mess we make… playing an essential role in purifying both our air and our water.

millipede invertebrate
Madagascar banded millipede (Aphistogoniolus polleni)

Life evolved sometime deep in the past history of our planet.

The invertebrates, being multicellular organisms, represent several steps along the road to the organisational complexity that makes us what we are.

After the evolution of the cell as the basis of life, the development of multicellular organisms, followed by the evolution of cellular organisation into tissues and organs all had to occur before we as human beings could exist.

Our wonderful lives – full of complex responses – our perceptions, emotions and thoughts are all only possible because of the highly evolved nature of our physical structure.

Perhaps you see evolution as the blind watch maker of writers like Richard Dawkins – conducting trillions of random experiments until eventually the answers that work are reached…

Or you may see evolution as the tool that a creator God used to unfold his design for life on this planet…

sea squirts on the reef
Sea squirts living on the reef

Whatever the case, the invertebrates remain our humble and unassuming ancestors. Well deserving of the few hours of your time it takes to become more familiar with the basics of their myriad lives.

I wish you well in your studies and hope you come to enjoy the beauty of the world around you more fully each and every day.

Learn More About Invertebrates

It is practically impossible to discuss the invertebrate phyla without some specialized terminology. There are two terms in particular which occur regularly: coelom and pseudocoelom.

To learn more about the individual invertebrate phyla you should browse through the big list of phyla of the animal kingdom below:

Otherwise, there are several phyla which may be of particular interest to you. Check them out below:

And in additional to this, there is a key subphylum and order (those lovable spiders) that you may wish to check out as well:


Gordon Ramel

Gordon is an ecologist with two degrees from Exeter University. He's also a teacher, a poet and the owner of 1,152 books. Oh - and he wrote this website.


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