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The structure of the diplosegments is normally hidden. In both living and preserved Polydesmida, the diplosegments 'telescope' into one another (image at right). This makes it difficult to see clearly just how they are built and how they are connected.
In fact, diplosegments, like haplosegments, are strengthened and thickened parts of the body tube (image below). However, diplosegments are much further from the simple tergite-pleurite-sternite pattern than are the haplosegments.



Lissodesmus perporosus (Dalodesmidae), Tasmania. This specimen has been treated with 80% lactic acid to dissolve away all soft tissue, and the gut has been removed. What remains (the exoskeleton) shows the trunk as a thin-walled tube with thickened sections, in this case the diplosegment rings.

The image at right gives a left ventrolateral view of a midbody ring. The ring is made up of a smaller-diameter, anterior prozonite (P) and a larger-diameter, posterior metazonite (M). There is usually a constriction or waist (w) where they meet.
The prozonite fits into the metazonite of the next ring towards the head. The only structure of note on the prozonite is a narrow line, here called the suture (su), which may represent a join between two elements in the manufacture of a new diplosegment (before each moult). The suture is more obvious in some Polydesmida than in others (see image below, left). It is often the place where sculpturing changes on the prozonite.
The metazonite has the ring's ozopores (o, if present) and spiracles (sp), and the sternite (st), to which the legs attach.



Noteremus summus
(suborder Dalodesmidea), Tasmania

Orthorhachis Unknown

Orthorhachis jubata (Dalodesmidae)
Queensland, Australia

Unidentified polydesmidan
Image © 2008 by Darren5907
Used with permission

Whether or not a diplosegment has the lateral extensions called paranota, the top of the metazonite is called the metatergite (image above, left). The metatergite is sculptured in many Polydesmida and often has transverse rows of setae. In some Polydesmida there is a transverse furrow (a shallow groove) on the metatergite. A furrow can be seen on each of the metatergites in the image above, right.

Back to: haplosegments
Forward to: paranota