The terms Vertebrates and Invertebrates were both coined at the dawn of the biology as a division of animals which have or do not have a backbone. The classification criteria have changed throughout the years, but these terms are still used though they have no longer scientific validity. It is the aim of this site to go deep into the specificity of the subject, so we will use these terms for the sake of simplicity.
The invertebrates form a very huge group which represent 95% of all animal species. Due to the fact of having no backbone this group encompasses animals with characteristics so different that they are grouped according to the complexity of the body structure from simple organisms like a sponge to articulate animales like a beetle. That is why we will divide the invertebrates into non arthropods (molluscs, annelids, etc) and arthropods (insects, arachnids, etc.).
The identification of invertebrates at species level is not so simple as that of birds or mammals. So, we will identify as precisely as possible. In case of doubt in the identification of a species, sp. will appear instead.
Non arthropods
Within this group the commonest examples to man are molluscs (snails) and annelids (worms).
Go to Arthropds