Spiders are one of the largest orders of the class Arachnida, which also includes the scorpions (Scorpiones), pseudo- or bookscorpions (pseudoscorpiones), havestmen (Opiliones), a variety of orders of mites and ticks (Acari).
Spiders can be recognised by a body consisting of two major parts, the cephalothorax (or prosoma) and the abdomen (or opisthosoma). They are the only group of animals with spinnerets at the back of their abdomen and in which males use modified, secondary organs, the pedipalps, to transfer sperm to the female. The morphology of the male pedipalps and the female copulatory organ, the epigyne, are crucial for identification, specifically at the species level.
There are approximately 4,000 species of spiders described from Australia, but this represents probably only about 25% of the total fauna. Framenau (2022) provides a checklist of all described species of Australia (download at the bottom of this page).