Acknowledgments

The following people must be thanked for their contributions to this key.  Ben Gunn (CSIRO Entomology), for his contribution of taxa and character images.  Gunther Theischinger (NSW Environmental Protection Authority), for the loan of many of the specimens that were used for photography. 

General Information

This intermediate-level key covers the huge and diverse phylum Arthropoda.

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).

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.

Some arthropods appear worm-like, notably apodous (maggot-like) insect larvae 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.

This Key to Arthropoda takes (1) minor groups directly to family level, (2) others to ordinal level or else to artificial but readily recognisable groupings, within which each component is then identified to family level in a separate key, (3) some Crustacean taxa to intermediate levels, in which families are recognised but not keyed.