According to Hedley, 500 species of Molluscs have already been counted in Australia. Among them is the gigantic Tridacna, 140 cm long. and 70 wide; like other tropical types, it is very widespread, but it is found especially in the Great Barrier Reef, a paradise for conchologists. As elsewhere, gastropods are the most numerous although many species of bivalves are also abundant, including oysters, of great present and future economic value, cephalopods, which include many species of Octopus, and large squid, which whales eat. spermaceti. In the waters of Sydney, and elsewhere as well, is the archaic Trigonia. Mother of pearl (Pinctada) abound in tropical waters and are highly sought after for commercial purposes.
Crustaceans are numerous and also have a great economic value. The various families of Macruri Decapods provide many forms of considerable size. Shrimps of the genus Penaeus (some very large) are also a source of lucrative fishing, carried out especially by Italian fishermen. A freshwater shrimp called yabbie (Parachaeraps) is found in large quantities in inland waters, although these are subject to drying up. Among the Brachiuri there are many species of crabs, from the smallest to the giant crab of Southeast Australia (Pseudocarcinus), in which only the flat part of the greater claw can measure up to 57 cm. Also well represented are the Anomuri or hermit crabs and, among the Arthrostraches, the Amphipods, some of which live in fresh water, and at least one species (Talitrus sylvaticus) among the damp leaves of the forests. Isopods are represented by many marine species, other fish parasites and an aberrant form (Phreatoicus) found in freshwater in Australia and Tasmania. Among the Entomostraches, the Cladocera and the Ostracods are probably the most abundant species in fresh water, but innumerable quantities of Copepods, Cladocera and Ostracods mainly constitute the planktonic fauna of the sea along the coasts. For Australia 1999, please check estatelearning.com.
But the unsurpassed wealth of Australian marine invertebrate fauna is impossible to give, in short, an adequate idea. Australia is certainly the region where corals (madreporarî) have their greatest development and to this environment of the madreporic banks there is a whole and rich fauna of other forms of Coelenterates, Echinoderms, Stars and Sea Anemones, Ascidians, Gorgonians, Sponges, Sea cucumbers, Annelids. The great sea anemone of the Great Barrier reaches a width of 60 cm.
According to Tillyard, Australia has more than 37,000 insect species. The richest order, as in general elsewhere, is that of the Coleoptera which has more than 17,000 species; then come the Lepidoptera, the Hymenoptera (including also a small indigenous bee) and Diptera. The order of the Embioptera, with few species, includes the archaic “weavers” similar to termites. The only orders not represented are the Proturi and the Zorapteri, rare insects discovered by Silvestri. Dragonflies are numerous in Australia, due to the abundance of more or less stagnant fresh waters. Among the Orthoptera the great bacillus which measures 45 cm should be remembered. Termites are very numerous, and their constructions can be very large. The so-called white ant of northern Australia builds a wall-shaped nest that is constantly oriented from north to south. Among the Hemiptera there are many species of cicadas and various aquatic species, one of which reaches 75 mm. Among the 8000 species of butterflies are the smallest and largest in the world, and some of the most beautiful.
Over 2000 species of Spiders are known in Australia. Among the most interesting are the trap-doors (Avicularidae), some of which reach considerable size and are very poisonous when biting. A species of the Licose family, which lives in desert regions, also builds a trap. A poisonous, red- backed spider (Latrodectus) is very common, even in arid areas. An Argiopid (Nephila) builds a yellow silk cloth strong enough to imprison even birds. Many ticks (Ixodina) infest indigenous and imported animals: an Ixodes attacks dogs and humans with sometimes lethal outcome. The fatal cattle tick (Boophilus) is however imported. Various scorpions abound in the rocky and wooded areas; they are generally small, the largest are found in the tropics.
Centipedes (Chilopoda) and millipedes (Diplopoda) are numerous. In tropical areas the former measure up to 20-22 cm. of length. A species of scolopendra abounds throughout Australia. Millipedes, according to Rainbow, number 60 species. A Spirobellus is numerous in eastern Australia, while a larger species (Dinematocricus), up to 10 cm long, is found in the north.