[Taxacom] Response to Dallwitz - part 3 (finish)

Bob Mesibov mesibov at southcom.com.au
Tue Sep 8 20:22:43 CDT 2009

Let's look at a specific example. I attach a drawing of a millipede gonopod (part of the male genitalia). The drawing was published in 2003 by a millipede taxonomist (not me). There is not, so far as I know, another organism on this planet that carries a structure that could be confused with this one. This drawing is both necessary and sufficient evidence for both circumscribing a species and identifying a gonopod-bearing specimen.

As it happens, this species is in a family whose *genera* can only very rarely be morphologically diagnosed or identified *without* reference to a drawing like this one. Not only do most species look much the same, but specimens of particular species vary enough in size, colour and other generalities that they could easily be confused with unrelated species. Females and juveniles - forget it, unless you do barcodes. But this is besides the point.

Now let's look at what the taxonomist wrote about this drawing. In the following quote I've inserted the a,b,c labels from the figure caption:

"Gonopods: (Fig. 6) Coxa well developed, crooked halfway. Prefemur relatively small, its axis making a distinct angle with the axis of the acropodite. Femoral process [c] rodlike, more or less shielded by the wide basal part of the solenomerite [b], ending in a series of slender spines of unequal length. Tibiotarsus [a] a simple elongate leaflike process, apically acuminate, curving in a laterodistal direction."

That's all the taxonomist wrote. I'm wondering what you think of that text. I suspect you think it lacks rigour, to put it mildly, and is a long way from being amenable to machine-assisted comparisons with other gonopods. I see the text differently. For me it's a pointer to a very few of the many, many things I can see in the drawing. It helps me as a comparative gonopod-ologist in ways I would have trouble explaining without reference to hundreds of other drawings.

So what could we do to make Dallwitz happy? Well, we could chuck the text out entirely and just have "Gonopod: see Fig. 6" in the description and a key. Alternatively, we could elaborate a detailed and explicit system of gonopod characters as text strings, then a detailed and explicit system of gonopod character states as text strings. We could then build a rigorous, machine-usable description, for which the drawing would only be supplementary data. Good luck. The homologies presumed above ("femoral process", etc) are uncertain and gonopods are spectacularly variable. Australian genera in the family concerned have gonopods with from 1-4 separate processes.

I'd prefer the wetware approach. I'd also like to point out that my wetware, processing that drawing, rapidly and accurately determines (a) which side of the male it was taken from, (b) what aspect it's drawn from and (c) what family of Polydesmida the species belongs to. Good stuff, this expertise, and not easily replaced by more 'reproducible' approaches to taxonomy.
Dr Robert Mesibov
Honorary Research Associate
Queen Victoria Museum and Art Gallery, and
School of Zoology, University of Tasmania
Home contact: PO Box 101, Penguin, Tasmania, Australia 7316
(03) 64371195; 61 3 64371195
Website: http://www.qvmag.tas.gov.au/mesibov.html

More information about the Taxacom mailing list