NOTE: The following information is also available under General Information when playing the key

BEST WAY TO USE THE KEY

The authors strongly recommend that users select Retain Uncertainties and Allow Misinterpretations from the Key menu.  Users will need a dissecting microscope for examination of all taxa, and a compound microscope for many of the groups.  This key allows identification of all subfamilies for water mites that are known from Australian inland waters.  Unless otherwise mentioned, locality records given in the taxon information come from Harvey (1998).

ABOUT THE TAXA

The Hydracarina, commonly called 'water mites', includes more than 5000 named species worldwide.  In Australia there are 413 described species in 89 genera, representing 22 families (Harvey 1998).  Larval water mites are 6-legged and are extremely heteromorphic relative to nymphal and adult mites.  This key is designed for identification of adults (which can be recognised by the presence of a genital opening); however, nymphs may be identifiable for some taxa.  Males can be differentiated from females by the presence of a complicated group of internal sclerites, the 'ejaculatory apparatus', associated with the genital opening. 

Water mites are parasitic on insects as larvae and are predatory as deutonymphs and adults.  A few taxa are parasitic on bivalves or crayfish in their postlarval stages (Walter & Proctor 1999).

PREPARATION OF SPECIMENS FOR IDENTIFICATION

Nymphal and adult water mites often make poor specimens if they are stored in ethanol for longer than a few days. Formalin is an even worse presevative as it makes the body of the mite rigid and difficult to clear.  Ideally, water mites should be killed, preserved and stored in Koenike's Fluid (10% glacial acetic acid, 50% glycerol, 40% water), also known as GAW (Harvey 1998).  This preservative keeps mites soft and flexible, and allows them to retain some of their original colour patterns.  Water mites that have been briefly exposed to ethanol usually make good specimens if they are rapidly transferred to Koenike's Fluid and left for several days to soften. 

Although many families and subfamilies of water mites can be identified from uncleared specimens, most require clearing.  Water mites are cleared in a solution of 10% KOH, and are returned to Koenike's Fluid when the body contents have become transparent.  If examination under a compound microscope is necessary, the body contents of the mite should be expelled through a small hole torn in soft membranes, and the deflated body of the mite arranged in a glycerine-filled cavity slide so that all appendages are visible (this may require dissection).  High quality permanent mounts of water mites are made in glycerine jelly (Cook 1974). 

USEFUL REFERENCES FOR AQUATIC MITES

Cook, D.R. 1976. Water mite genera and subgenera. Mem. Amer. Ent. Inst. 21: 1-860.

Cook, D.R. 1986. Water mites from Australia.  Mem. Amer. Ent. Inst. 40: 1-568.

Harvey, M.S. 1998. The Australian water mites: a guide to families and genera. CSIRO Publishing, Collingwood, Victoria.

Walter, D.E. and H.C. Proctor. 1999. Mites: ecology, evolution and behaviour.  University of New South Wales Press, Sydney, New South Wales.

ABOUT THE AUTHORS

Mark Harvey is Curator of Arachnids at the Western Australian Museum, Perth, WA.  Heather Proctor is a lecturer in the School of Environmental Studies, Griffith University, Brisbane, QLD.