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Polydesmida: Atalopharetra and Bromodesmus

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The eight species in the endemic H+20 genera Atalopharetra and Bromodesmus have gonopods on which the solenomere (the structure with the 'delivery end' of the sperm canal) is protected by a broad hood. Both genera also have species with a powerfully smelling defensive secretion (bromos is Greek for 'stink'). Whether the two genera are genuinely close relations isn't known yet, but it's a curious fact that they divide up Tasmania rather neatly between them, as shown in this map:

Tasmania mapBrachydesmus

Combined localities for Atalopharetra species (red) and Bromodesmus species (blue). A. johnsi and B. rufus come close to meeting between Tarraleah and Victoria Valley in central Tasmania. 



Atalopharetra

Atalopharetra

The surface-dwelling species Atalopharetra bashfordi and A. johnsi are ca 25 mm long and live in the wet forests of southwestern and southern Tasmania. Both species burrow in richly organic soils and are only rarely seen in leaf litter or rotting logs, although both have been pitfall-trapped. The two species have broadly overlapping ranges in the Southern Forests, and they cannot (yet) be separated without examining the gonopods of mature males. There are many Atalopharetra localities not shown on the maps because the only specimens found were female or juvenile.


gonopodsbashfordi

A. bashfordi (rear view)

gonopodsjohnsi

A. johnsi (rear view)

 

 

A. clarkei and A. eberhardi are cave-dwellers with the usual range of troglomorphic features: pale colour, thin body and unusually long legs. In contrast to the surface-dwelling Atalopharetra species, the cave-dwellers have well-developed paranota (see 'anatomy' images below) and A. eberhardi is armoured with an abundance of paranotal teeth. A. clarkei is so far known only from caves near Ida Bay, while A. eberhardi has been collected in caves near Precipitous Bluff.


gonopodsAtalopharetra

Left paranotal margin of midbody ring of A. clarkei (left) and A. eberhardi (right), and rear view of A. clarkei gonopods (centre)

Mesibov (1997b, 1998c, 2005b)


Tasmania mapbashfordi

A. bashfordi
Mesibov, 2005

Tasmania mapclarkei

A. clarkei
Mesibov, 2005

Tasmania mapeberhardi

A. eberhardi
Mesibov, 2005

Tasmania mapjohnsi

A. johnsi
Mesibov, 2005 



Bromodesmus

Bromodesmus

Adult females of (left to right) Bromodesmus catrionae, B. militaris, B. riparius and B. rufus. Scale bar = 10 mm.

Bromodesmus was formerly code-named 'Rankodesmus' because of the very strong-smelling defensive secretion in B. catrionae. The secretion can also stain specimens a red-brown colour after long storage in alcohol, as seen with B. catrionae and B. militaris in the image above. Fresh specimens of these two species are pale brown to gray-brown with dark-brown banding around each ring.

All four Bromodesmus species burrow deep in the soil, but B. rufus can sometimes be found in or under woody litter. B. rufus is also a true subalpine millipede, with a known elevation range to ca 1300 m. B. riparius can be abundant in rich organic soil close to shaded streams in the Dial Range, but seems to be rare elsewhere. Note in the maps that there is almost no overlap among the four Bromodesmus species ranges. This will help with identification, but be sure to check the male gonopods, shown below.


gonopodsB. riparius

Gonopods of B. riparius (head to left). In this specimen the gonopod bases have 'emerged' from the body


gonopodsBromodesmus

Gonopod tips (left to right) of B. catrionae, B. militaris, B. riparius and B. rufus. In some specimens of B. riparius the needle-like solenomere points straight up.

Mesibov (1997c, 2004b)


Tasmania mapcatrionae

B. catrionae
Mesibov, 2004

Tasmania mapmilitaris

B. militaris
Mesibov, 2004

Tasmania mapriparius

B. riparius
Mesibov, 2004

Tasmania maprufus

B. rufus
Mesibov, 2004