Size

Agathodesmus steeli
Haplodesmidae; New South Wales, Australia
5 mm long
Hover cursor over image for close-up

Barydesmus sp. (Platyrhachidae),
Peruvian Amazon, 100 mm long
Tentatively identified from this image
by R.M. Shelley and D.M. Torres
Image © 2005 by Dan Rosenberg
Used with permission

Size can also vary within a species. The image at right shows two adult females of Lissodesmus hamatus (Dalodesmidae), a common species in eastern Tasmania. The larger female is from high-rainfall forest, and the smaller female is from low-rainfall woodland. Scale bar = 10 mm.

A good way to record polydesmidan sizes is with the two measurements shown at right. d is the maximum diameter of a diplosegment (posterior view), and mw is the maximum width of a ring, including the paranota.
 
Which body ring should you measure? Many published descriptions give figures for a 'midbody' ring, which is a ring roughly halfway along the length of the body. You can also specify which ring you measure, for example
 
...maximum diameter of ring 10, 1.9 mm;
maximum width across ring 10 paranota, 2.6 mm...