Introduction

This publication is part of a planned key to nematodes of Australia. It is not currently available as CD-ROM. If users would like the key published as CD-ROM, please contact the author. If there is sufficient interest, it may be possible to publish in this format.

The package is generated from a DELTA database (Dallwitz 1980, Dallwitz et al. 1993). It comprises an interactive identification and retrieval system using the program INTKEY (Dallwitz et al. 2000), descriptions, illustrations, references, and other subsidiary material. It allows users to obtain:

• Identifications of nematodes from the Murray-Darling River System and coastal freshwaters of southeastern Australia to generic, and occasionally species level, with the assistance of character notes and images;
• Identifications of some nematode genera from out of the defined area;
• Identifications of species of the genus Pratylenchus (Root Lesion Nematode) known from Australia;
• Determination of life stage and sex of a nematode specimen;
• Information on synonymy, classification, distribution, ecology and biology, with bibliographic references;
• Diagnostic or full descriptions of any taxon;
• Lists of taxa having particular attributes (eg long tails);
• Images of at least one life stage for overall body, and detail of body structures.

Nematodes are the most abundant and ubiquitous multicellular organisms on earth. They are found from the bottom of the deepest ocean to near the tops of the highest mountains, from the tropics to polar regions, and from every conceivable habitat. Nematodes are also found in or on most other types of organisms as parasites, commensals or phoretics: everything from earthworms, insects, molluscs, fish, reptiles birds, mammals to humans. In fact it is said that if the everything on the earth were to disappear except the nematodes, the outlines of everything would still be visible: the mountains, lakes and oceans, the plants and the animals would all be outlined by the nematodes living in every habitat.

Nematodes are also amongst the most diverse taxa on earth, with an estimated 500 000 to 1 000 000 species. Only about 20 000 species have been described, and the systematic literature is widely dispersed. It is hoped this key will fill some of this void.

Nematodes range in size from nearly 10 metres long to only a fraction of a millimetre. They are mostly worm-like in shape, but some are spherical, lemon-shaped, sausage-shaped and a host of other variations. In diameter, they range from a few millimetres to about 5 microns.

 

Although they are small, nematodes are incredibly abundant. If all the nematodes in the Murray River were combined into one huge animal, it would be over 20 metres long (see image left). Laid end-to-end they would encircle the earth’s equator. Nematodes are even more abundant in terrestrial, estuarine and marine substrates.

Nematodes impact on human economies in many ways: from loss of agricultural production, to pasture and turf damage, to invasion of forest trees, to adverse effects on the health of wild and domestic animals and humans. In addition to causing losses, there are many beneficial effects of nematodes: controlling soil nutrient cycling and controlling harmful species to name just two. The total value of these economic effects are difficult to quantify, but must be very substantial indeed if one considers that the lost production to just one crop (wheat) in just one country (Australia) is estimated at $200 million per annum. Illustrated at right is the effect of plant parasitic nematodes on a canola crop.

Because of their ubiquity and diversity, nematodes are also used in measuring the impacts of various perturbations on ecosystems, such as pollution, organic enrichment, and physical disturbance. Nematodes are intimately involved in many parts of the soil ecosystem, so they can be used as indicators of sustainability for soils.

It is hoped that this identification system will assist both those studying nematodes as part of other problems, as well as those studying them in their own right.

The Database

This database consists of a set of about 50 genera, each of which is coded for over 600 characters with from 1 to 11 character states (usually 2 or 3), plus additional characters which include geographic and ecological distribution, general biology (feeding habits etc.), alternative name(s) (synonymy), a list of references, and miscellaneous notes. Juveniles, adult females, adult males, and populations of each genus are coded separately. In a few cases, species are distinguished where this facilitates identification.

The Character Set

This interactive tool and database has been developed to meet the needs of a wide variety of users, so the characters included range from those easily observable with minimal magnification (eg. relative lengths and widths of major body parts) to those requiring the highest optical magnifications possible (oil immersion). Characters requiring electron microscopy have been omitted. There is no explicit "weighting" of characters so that easy characters appear near the top of the "best" list of characters, rather there are simple means to change the set of characters from which to choose at any time.

Many characters are coded in a non-phylogenetic way to assist in identification. Thus, for example, there is a character for presence or absence of setae on the head, so that a user does not have to distinguish whether they are phylogenetically from the first or second labial whorl or from the several cephalic whorls.

Often there are different forms of the same character. There may be one character for present or absent, another for conspicuous or inconspicuous (the latter including present but very small), and another for the number of structures (which can be zero, meaning absent). Thus a user who lacks facilities or is uncertain of the presence or number of a small feature, can choose the character state "inconspicuous" in the second of the characters listed. A user with advanced equipment and the experience to definitely count such a feature could enter the exact number. Some structures are distributed around the circumference of nematodes, so counting an exact number may not be feasible and in some situations an exact count is not necessary.In either of these cases presence or absence may be the best way to use a character.If an alternative character or character coding is not available and there is doubt, two or more states can be selected instead of one.

Characters requiring a measurement or the ratio of measurements may appear as characters to avoid, however because of the high internal pressure an inextensible cuticle of nematodes, they can be very useful on appropriate specimens (see below under Sources of Data). These characters can rapidly eliminate many potential taxa because the variation in size and body shape in nematodes is large. A range of measurements or ratios can be used (eg. 2-5 mm, 1.6-1.9), the figures do not have to be exact, and the Windows Calculator can be accessed to assist with calculations.

Sources of Data

All data was obtained from specimens collected specially for the purpose. Character states were coded from heat-relaxed specimens preserved in 3% Formaldehyde and dehydrated to pure glycerol. The key should also work with live narcotized or recently heat killed specimens which are not fixed. Characters involving measurements should not be used on specimens which have been in fixatives containing alcohol, which causes considerable shrinkage and distortion. Specimens which have been in alcohol can be identified using only characters not involving measurements, size or shape, but more and harder characters may be required for identification.A brief description of methods for fixing nematodes is included in the key (under the heading “Techniques” accessed from the “Introduction and References” button on the toolbar).

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