What is an invertebrate?

What is an invertebrate?

The short answer is that Invertebrates are animals without a backbone.

There is a good chance that you have seen an invertebrate recently. Do you recall batting away a fly, unearthing a worm, or admiring a spider as it waited to catch food in its web. Well guess what? All of these animals and many more are collectively known as invertebrates - animals that lack a backbone.

Invertebrates are everywhere

There are so many invertebrates on this planet that it is impossible to count them all. They come in many shapes and sizes, live practically anywhere and provide many services that are vital for our survival.

Invertebrates have been recorded in the upper reaches of the atmosphere, in the driest of deserts and in the canopies of the wettest rainforests. They can even be found in the frozen Antarctic (some mites and springtails can withstand temperatures of -35°C) or on the ocean floor of the Abyssal Sea which reaches depths of up to 11 000 metres.

Invertebrates are all around us and yet amazingly most go about their daily business unnoticed. Much of this has to do with the size of invertebrates. On land, invertebrates range from fractions of a millimetre to approximately 150 centimetres in length, though most are less than five centimetres. Their size allows them to occupy large habitats such as deserts and rainforests as well as many microhabitats, which may not be visible to the eye. For example, they may be found in a pool of water in a pitcher plant, the follicles of a hair, or inside a seed.

Of the planet's estimated 15-30 million animal species, 90% or more are invertebrates. Invertebrates live just about anywhere. They have been recorded in the upper reaches of the atmosphere, in the driest of deserts and in the canopies of the wettest rainforests. They can even be found in the frozen Antarctic or on the deepest ocean floor.

Invertebrate groups

Terrestrial (land) invertebrates include the following groups, many of which also have members that live in freshwater or marine environments:

• Insects
• Spiders
• Centipedes
• Millipedes
• Worms
• Velvet worms
• Slaters
• Landhoppers

Marine and freshwater invertebrates include the following groups, some of which have land-dwelling members also:

• Snails and slugs
• Sea stars and sea urchins
• Anemones and corals
• Crabs, lobsters, prawns and crayfish
• Sponges
• Bluebottles, jellies and comb jellies

Australian land invertebrates

It is estimated that Australia has 275 000 to 300 000 species of invertebrates that live on land. Many of these species are endemic to Australia (not found anywhere else in the world).

More than 80% of all the cicadas, leafhoppers, true bugs and ants found in Australia are endemic. The high level of endemism is attributed to a number of factors:

1. Australia has a long geological history of isolation from other continents.
2. Australia is large and consequently has a wide range of habitats including tropical, temperate, semi-arid and arid regions.
3. Australia has a landscape dominated by many different species of endemic flora. Invertebrates have exploited the many food sources and niches that these plants offer. As a result it is estimated that a third of all foliage feeding insects in Australia depend on our native Eucalypts and Acacias.

Despite the uniqueness of Australian invertebrates we unfortunately know little about them. Scientists believe that less than 15% of our invertebrates have been formally described. This is concerning when we consider the current rate of habitat destruction in this country. Through the removal of these precious habitats we maybe destroying countless species of invertebrates that we are not aware of.