Most animals, in terms either of numbers of individuals, or of number of species are invertebrates. Of the 34 phyla of animals in the Kingdom Animalia 32.5 of them are invertebrates in that they are lacking a spine or vertebra, 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 many of the phyla (20) contain only a few, less than 500 species, explains why we often remain unaware of this wonderful diversity of life that shares our planet with us.
These invertebrates, in 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.
Life evolved sometime deep in the past history of our planet, the invertebrates, in 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. Whether 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 if you see evolution as the tool that a creator God used to unfold his design for life on this planet 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.
It is practically impossible to discuss the invertebrate phyla without some specialised terminology, there are some terms which occur regularly and I have tried to explain them in a separate page here called coelom.html. I hope eventually to have a fully glossary associated with this site, however that is for the future.
To learn more about the individual phyla you will need to visit the page an-phyla.html
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.
No person can be an expert at everything and I am in fact an expert at nothing, a bibliography of the Books I have used in the construction of this and other Earthlife Web sites is available at Bibliography I am indebted to all the authors for the work they have put in to make this information available to me. I am sorry there is no hope of my getting the list of papers typed up in the near future. However I would like to acknowledge the invaluable help I have received from a wide variety of individuals, on the many scientific discussion lists to which I belong, who have patiently helped sort out particular problems. In particular I would like to thank Dr. Alvaro E. Migotto of the 'Centro de Biologia Marinha' - Universidade de São Paulo, Brazil, for the beautiful photos he kindly donated and which adorn a number of the individual pages associated with this site.