See Key to Orders of Australian Aquatic Arthropoda
Arthropoda is a huge and diverse phylum and forms a conspicuous component of the macroinvertebrate fauna in most aquatic environments.
Arthropods have in common a segmented body which is differentiated into regions, an external chitinous cuticle, and paired jointed appendages (as gills, swimming organs, walking legs, antennae, chelicera, etc.). Appendages may be absent in some juvenile forms. The mouth is more or less anterior, the gut usually straight and the anus sub-terminal. The nervous system is patterned on a dorsal brain with paired ventral nerve cords and paired ganglia in each body segment. An open, dorsal heart circulates haemolymph around the body cavity.
The major classes of arthropod found in inland waters are Crustacea (all life stages) and Insecta (adults and/or larvae and/or pupae). Lesser components of the fauna include Arachnida (mites, spiders), Myriapoda (millipedes) and Collembola (springtails).
Identification to Arthropoda usually can be based on body form and the presence of jointed appendages. Some apodous (maggot-like) insect larvae appear worm-like, although the body always is clearly segmented and there almost always is a well-developed head with biting, jointed mouthparts. In some families of Diptera (true flies) the larvae are legless, eyeless, and apparently headless (the head is small and retractile). Paired unjointed prolegs, hooks, gills or other appendages often are present in these species.
For further identification of Arthropoda the Key to Arthropoda takes minor groups to family level, and the remainder to ordinal level or else to artificial but readily recognisable groupings. Each component is then dealt with to family level in a separate key.