Fauna of Australia - Invertebrates

Invertebrates

Of the estimated 200,000 animal species in Australia, about 96% are invertebrates. While the full extent of invertebrate diversity is uncertain, 90% of insects and molluscs are considered endemic. Invertebrates occupy many ecological niches and are important in all ecosystems as decomposers, pollinators, and food sources. The largest group of invertebrates is the insects, comprising 75% of Australia's known species of animals. The most diverse insect orders are the Coleoptera, with 28,200 species of beetles and weevils, the Lepidoptera with 20,816 species including butterflies and moths, and 12,781 species of Hymenoptera, including the ants, bees and wasps. Order Diptera, which includes the flies and mosquitoes, comprises 7,786 species, Order Hemiptera, including bugs, aphids and hoppers, comprises 5,650 species; and there are 2,827 species of order Orthoptera, including grasshoppers, crickets and katydids. Introduced species that pose a significant threat to native species include the European wasp, the red fire ant, the yellow crazy ant and feral honeybees which compete with native bees.

Australia has a wide variety of arachnids, including 135 species of spider that are familiar enough to have common names. There are numerous highly venomous species, including the notorious Sydney funnel-web and redback spiders, whose bites can be deadly. There are thousands of species of mites and ticks from the subclass Acari. Australia also has eight species of pseudoscorpion and nine scorpion species.

In the Annelida (sub)class Oligochaeta there are many families of aquatic worms, and for native terrestrial worms: the Enchytraeidae (pot worms) and the "true" earthworms in families Acanthodrilidae, Octochaetidae and Megascolecidae. The latter includes the world's largest earthworm, the giant Gippsland earthworm, found only in Gippsland, Victoria. On average they reach 80 cm in length, but specimens up to 3.7 m in length have been found.

The large family Parastacidae includes 124 species of Australian freshwater crayfish. These include the world's smallest crayfish, the swamp crayfish, which does not exceed 30 mm in length, and the world's largest crayfish, the Tasmanian giant freshwater crayfish, measuring up to 76 cm long and weighing 4.5 kg. The crayfish genus Cherax includes the common yabby, in addition to the farmed species marron and Queensland red claw. Species from the genus Engaeus, commonly known as the land crayfish, are also found in Australia. Engaeus species are not entirely aquatic, because they spend most of their lives living in burrows. Australia has seven species of freshwater crab from the genus Austrothelphusa. These crabs live burrowed into the banks of waterways and can plug their burrows, surviving through several years of drought. The extremely primitive freshwater mountain shrimp, found only in Tasmania, are a unique group, resembling species found in the fossil record from 200 MYA.

A huge variety of marine invertebrates are found in Australian waters, with the Great Barrier Reef an important source of this diversity. Families include the Porifera or sea sponges, the Cnidaria (includes the jellyfish, corals and sea anemones, comb jellies), the Echinodermata (includes the sea urchins, sea stars, brittle stars, sea cucumbers, the lamp shells) and the Mollusca (includes snails, slugs, limpets, squid, octopus, cockles, oysters, clams, and chitons). Venomous invertebrates include the box jellyfish, the blue-ringed octopus, and ten species of cone snail, which can cause respiratory failure and death in humans. The crown-of-thorns starfish usually inhabits the Reef at low densities. However, under conditions that are not yet well understood, they can reproduce to reach an unsustainable population density when coral is devoured at a rate faster than it can regenerate. This presents a serious reef management issue. Other problematic marine invertebrates include the native species purple sea urchin and the white urchin, which have been able to take over marine habitats and form urchin barrens due to the over harvesting of their natural predators which include abalone and rock lobster. Introduced invertebrate pests include the Asian mussel, New Zealand green-lipped mussel, black-striped mussel and the Northern Pacific seastar, all of which displace native shellfish.

There are many unique marine crustaceans in Australian waters. The best-known class, to which all the edible species of crustacean belong, is Malacostraca. The warm waters of northern Australia are home to many species of decapod crustaceans, including crabs, false crabs, hermit crabs, lobsters, shrimps, and prawns. The peracarids, including the amphipods and isopods, are more diverse in the colder waters of southern Australia. Less-well-known marine groups include the classes Remipedia, Cephalocarida, Branchiopoda, Maxillopoda (which includes the barnacles, copepods and fish lice), and the Ostracoda. Notable species include the Tasmanian giant crab, the second largest crab species in the world, found in deep water, and weighing up to 13 kg, and the Australian spiny lobsters, such as the Western rock lobster, which are distinct from other lobster species as they do not have claws.