What is an invertebrate

A.� An invertebrate is any animal that doesn't have a backbone. Invertebrates make up the majority of the animal kingdom, both in terms of number of species overall and individual numbers.

�

Although most of the animals we are familiar with, mammals, birds and fish, seem the more prevalent, these animals, which belong to the chordates (backbone) phylum, and comprise a relatively small number of animals.

�

Of the estimated 800,000 species identified so far, the majority are invertebrates, 100,000 alone are worms, virtually unknown to anyone except specialists.

�

Q.� Estimated

A.� Yes, the actual number of living species isn't known.

�

Q.� Ah, so there might be some unknown vertebrates waiting to be discovered

A.� One or two possibly, especially deep-sea fish, but the majority of as yet unidentified species are invertebrates.

�

Q.� Could their discovery drastically boost the figures

A.� Yes, scientists estimate that if all the species in a tropical rainforest were identified then there would be an extra 10 million species, mainly belonging to the arthropod phylum, which is made up of insects, spiders and scorpions.

�

Q.� What's a phylum

A.� It's the highest divisional point of the animal kingdom. Basically animals are separated into more and more distinct categories according to their characteristics. Things start off quite general at the top, for example, animals with or without a backbone, get more specialised, for example animals that produce live young which they breast feed, the mammals, down to the specific defining characteristics of a species, for example animals that walk on two legs and have large brain, Homo sapiens.

�

To read more about the classification of living organisms, click here.

�

Of the 33 sub phyla only one isn't for invertebrates, it has 45,000 species, leaving 755,000 invertebrate species.

�

Q.� Which invertebrate phylum has the most species

A.� This award goes to the Arthropods, which includes spiders, scorpions, insects and crustaceans, which has at least 500,000 species although scientists estimate the real number could be as high as 10,000,000.

�

Got a question about the animal kingdom Click here to ask.

�

by Lisa Cardy