Note: information below is also available under General Information,
which can be accessed while running the Key.
BEST WAY TO USE THE KEY
For best results in keying specimens, the
authors strongly recommend that users select both Retain
Uncertainties and Allow Misinterpretations
from the "Key" menu by placing a checkmark beside each option.
Users will need a dissecting microscope for examination
of all taxa, and a compound microscope for many of the mite groups.
This key allows identification of all families of arachnids (and
subfamilies for water mites) that are known from Australian inland waters.
Water mite families and subfamilies are identified in a subkey
associated with the taxon Hydracarina.
ABOUT THE TAXA
The Arachnida belongs to the Phylum Arthropoda,
Subphylum Chelicerata, and is typically placed at the level of Class.
Arachnids are characterised by having 4 pairs of legs as adults and
lacking antennae. Their mouthparts
are chelicerae; however, only some arachnids retain the ancestral chelate
(pincer-like) form of the chelicerae, while other groups have hook-like or
There are two major groups of arachnids that have
aquatic representatives: the spiders (Order Araneae)
and the mites (Subclass Acari).
Species from four families of spiders may be encountered in Australian
fresh waters. Despite being able to
survive for some time under water, none of these spiders is truly subaquatic.
The vast majority of aquatic arachnids are mites.
Larval mites are 6-legged and are often morphologically very different
from the 8-legged nymphal and adult mites.
This key is designed for identification of post-larval stages; however,
it may work for larvae of some groups of mites.
Representatives of four major suborders of mites occurs in fresh water: Mesostigmata,
(Walter & Proctor 1999). The
greatest radiation of freshwater mites has been in the prostigmatan group Hydracarina
(also called Hydrachnellae, Hydrachnidia, Hydrachnida). 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
PREPARATION OF SPECIMENS FOR IDENTIFICATION
Identification of arachnids other than spiders often
requires special preparation.
(a) Spiders, non-hydracarine mites, and the larvae of
water mites: specimens from these groups may be preserved in 70-80% ethanol.
Non-hydracarine mites should be cleared in lactic acid or Nesbitt's
Fluid, and then placed in glycerol in a cavity slide for examination under a
compound microscope. Permanent
mounts can be made with Hoyer's Fluid or polyvinyl alcohol preparations (Krantz
(b) Nymphal and adult Hydracarina: these 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
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.
Krantz, G.W. 1978. A manual of acarology. 2nd edition.
Oregon State University Book Stores, Corvallis, Oregon.
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
composed by Brendan Mckie
with helpful comments from Robert Raven (Queensland Museum).
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. David
Walter is a senior lecturer in the Department of Zoology and Entomology,
University of Queensland, Brisbane, QLD.