Key to Phylum and Class of Australian Aquatic Invertebrates

Phylum and class of Australian Aquatic Invertebrates home pageThis is the central key in this series of linked Keys to Australian Aquatic Macro-Invertebrates.  The key is designed to identify any specimen to a level corresponding approximately to Phylum or Class.

For most major invertebrate groups this key points directly to a family-level subkey.  For arthropod taxa, it points to a Key to Arthropoda as an intermediate-level key.  Groups for which no subkey is provided can be identified further using the notes and illustrations given against the relevant terminating taxon in this key.  In most cases, these notes allow identification to family level, but a few taxa, namely rotifers, gastrotrichs and nematodes, are taken only to ordinal level.


This set of keys was prepared mainly from the primary and secondary taxonomic literature and from existing dichotomous keys.  Expert advice and assistance was sought in some cases.  References and acknowledgments with respect to each key are given in the text which accompanies that key.

Taxon coverage

These keys cover the free-living macroscopic invertebrate taxa known to occur in Australian inland waters, including introduced taxa.  Taxa represented in fresh or saline, running or still, permanent or ephemeral inland waters are included, but wholly marine taxa which may extend into upper estuarine habitats, and wholly terrestrial taxa some species of which extend into intermittently wet habitats, have generally been omitted from the keys.

The aim has been to key free-living organisms to family level.  Only higher-level identification is provided for (i) taxa in which all species are obligate parasites, (ii) taxa mainly comprised of organisms too small to be retained by a 250mm mesh sorting sieve, and (iii) semi-aquatic, damp-soil and semi-marine (upper estuarine) taxa.

Some taxa are not taken to family level because the taxa are poorly known.  For these the key runs to whatever level can be achieved on current knowledge.  For example, phylum Nematoda is taken only to order (and then only by way of taxon notes) and part of Platyhelminthes is taken only to superfamily level.

Geographic coverage

Our aim has been to cover the whole of Australia, but not all source documents specify whether offshore territories, etc, are included.  Thus, coverage of tropical/subtropical island territories, and Antarctic/sub-antarctic territories may not be complete for some taxonomic groups.

Ecological coverage

Our aim has been to cover all inland waters: fresh or salt, flowing or still, including marshlands and temporary waters.  The dividing line between riverine and estuarine habitats is hazy, as are also the line between marine littoral and coastal saltmarsh and that between wetlands generally and damp terrestrial environments.

At genus or species level the decision what to include or exclude could be problematic, but at family level it is less so.  For the most part, families which are strongly represented in marginally-aquatic environments also include one or more truly aquatic species, and thus are included in the keys.  Where this is not the case we err on the side of including taxa which might be found in aquatic samples.  Where sources differ as to whether a family has aquatic members we treat it as if it has.


The idea behind an interactive key is to identify a specimen by eliminating all the taxa to which it cannot belong.  Identificatory characters may be taken in any order convenient to the user.  The first character in the present key (character one when the characters are listed in Lucid natural order) exemplifies the method but is somewhat unusual in that it asks for a first impression (gestalt) of the specimen.  Most other characters are more specific.  Some specimens can be identified to a single taxon on the basis of gestalt but most cannot.  For example, medusoid jellyfish are instantly recognisable as such, but flatworm-like animals occur in many phyla apart from Platyhelminthes.  By selecting ‘jellyfish’ all taxa except Cnidaria would be eliminated; by selecting ‘flatworm’ taxa such as Bryozoa and Porifera would be eliminated, but further characters would be needed to reduce the list which remains.

Throughout these keys, character codings have been written so as to retain every taxon which has, looks as if it has, or might reasonably be mistaken as having the attribute in question.  For this reason it would be inappropriate to take the attribute codings from these keys and to read them as if they represented a true description of the taxon.  Identificatory character attributes are not character states in the conventional sense.  They deal with specimens not taxa.  Their totality is not a valid description of the taxon to which an identified specimen belongs.


Errors in and omissions from these keys should be referred to Peter Cranston ([email protected]) but most of the blame lies with John Trueman ([email protected]).


Keys prepared at CSIRO Division of Entomology, Black Mountain Laboratories, PO Box 1700, Canberra, ACT 2601, AUSTRALIA

By Ben M. Gunn, John W.H. Trueman, Sophia Dimitriadis and Peter S. Cranston, with funding from the Land and Water Resources Research and Development Corporation, Inc.