The following people must be thanked for their contributions to this key.
Ben Gunn (CSIRO Entomology), for his contribution of taxa and character
images. Brian Smith (Queen Victoria
Museum & Art Gallery) and Mick Smith (W.A. Department of Conservation &
Land Management), for the loan of many of the specimens that were used for
photography. Winston Ponder provided the images of Glacidorbidae,
Hydrococcidae, Iravadiidae and Mytilidae. Keith
Walker receives special mention for his contribution of a text-based key to the
Australian Mussels and SEM images of Hyriidae glochidium larvae.
This large phylum is divided into several classes of which only the
Bivalvia (bivalved molluscs) and Gastropoda (snails and slugs) are found in
Bivalved molluscs occur commonly in marine and estuarine environments.
Four families are known from Australian inland waters.
Identification to Bivalvia is relatively easy based on the bi-valved
shell which covers the whole body, but care should be taken, especially with
small specimens, to check the animal is not a crustacean of class Conchostraca
(clam shrimp) Ostracoda (mussel-shrimp or seed-shrimp), or Cladocera (water
flea). These animals have a
bi-valved carapace and may superficially resemble bivalved molluscs, but within
the carapace is a shrimp-like body with several pairs of jointed legs.
The four freshwater bivalve families are:
1 Hyriidae (Freshwater mussels)
A family restricted to South America and Australasia.
Found throughout mainland Australia and central-north Tasmania,
absent from southern Tasmania. Some
species are endemic to particular catchments whilst others are cosmopolitan.
The first larval stage is the minute, bivalved glochidium, ectoparasitic
on the gills, fins, or general body surface of various fish.
2 Corbiculidae (Orb-shell mussels)
Found in Asia, Australia and Oceania, with isolated introductions in
other parts of the world. A
tropical to subtropical group. There
are two distinct species groups in Australia.
The first (genera Batissa and Polymesoda) inhabit fresh and
estuarine coastal streams of northern Australia, and are closely related to
forms found in south-east Asia. The
second (genus Corbicula, endemic subgenus Corbiculina) are found
throughout Australia except for Tasmania and the southern part of Western
(Pea shell mussels, pea shells, fingernail clams)
A little studied but cosmopolitan family of small bivalves.
Previously, many names were based on minute differences in the shell and
on geographic distribution. Some
species are widespread throughout Australia but others are confined to small
regions or in some cases to a single body of water.
The cosmopolitan family which includes the marine mussels.
Several species are estuarine and some may be found in near-fresh water,
but never entirely away from marine influence.
Identification to family can be based on the shell. The Hydriidae and Mytilidae are elongate mussels with the beak of the shell at one end. Corbiculidae and Sphaeriidae are sub-circular. Hydriid larvae (glochidium larvae), parasitic on freshwater fish, are keyed separately in this key
The aquatic gastropod families divide into two subclasses, the
gill-breathing Prosobranchia are related to marine snails, the lung-breathing
(or secondarily gilled) Pulmonata are related to land snails.
Eleven prosobranch families and nine pulmonate families are recorded from
Australian inland waters.
Almost all species are shelled and recognisably snail-like, but one
family (Onchidiidae) of marine, air-breathing slugs extends into estuaries and
damp terrestrial situations near the sea.
Identification to class Gastropoda is relatively easy based on the
snail-like shell and/or the presence of a pulmonate lung in the mantle cavity.
Larvae of Helicopsychidae, a family of caddis-fly (Insecta: Trichoptera)
construct a helical case which resembles a snail shell, and could be mistaken
for molluscs. The trichopteran case
is composed of sand grains and the animal inside is a typical insect larva with
segmented body and three pairs of legs.
The identification of gastropods to family level can be difficult because
the families are defined on internal anatomical structures.
There are few readily observable characters, other than those of the
shell, but shells vary as much within as between families.
Adult whole animals can be identified using a combination of shell (and
operculum) plus external body characters, but juveniles and shells alone are not
always identifiable to the family level.
Character systems useful for identifying gastropod families include:
1 Shell coiling (dextral, sinistral, flat, or not-coiled)
2 Operculum presence/absence
3 Shell shape (spired, globose, turbinate, etc.) and spire
4 Shell patterning (ridges, striations, colour patterns,
5 Tentacle and eye position
Some species will key easily to family level, but others may be
McMichael, D.F. (1967) Australian freshwater Mollusca and their probable
evolutionary relationships: a summary of present knowledge. pp. 123-149.
In: Weatherly, A.H. [ed.], Australian
Inland Waters. Australian
National University Press, Canberra.
Smith, B.J. and Kershaw, R.C. (1979) Field Guide to the Non-Marine Molluscs of South-Eastern Australia. Australian National University Press, Canberra.