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Photo#727230
Siagonium punctatum male, dorsal - Siagonium punctatum - male

Siagonium punctatum male, dorsal - Siagonium punctatum - Male
Sandia Mountains, Bernalillo County, New Mexico, USA
September 19, 2012
Size: 4.9 mm
Download high resolution image here.

I collected this beetle on 10K Trail (No. 200) at 10,000 ft. elevation, Sandia Crest 7.5’ quadrangle in the Sandia Mountains, Bernalillo Co, NM from a Berlese funnel loaded with forest floor detritus collected from under and around a rotting log in a conifer forest.

This post complements Jeff Gruber's fine images, and documents S. punctatum's occurance and appearance in the US Southwest. Moore 1975's key(1) identifies it as S. punctatum based on its 5 punctate elytral stria and mostly smooth, but partially strigulose pronotum. The desciption above his key states, "Some specimens of S. punctatum, particularly from Arizona, have partially longitudinally strigulose pronota". New Mexico is Arizona's eastern neighbor, and such strigula (fine lines) can be seen on the pronotum near the anterior left and right corners. The pronotum length to width ratio, another cited identifying characteristic consistent with S. punctatum, is 0.75 for the subject specimen. Also, his distribution map records S. punctatum as being the only member of this genus found in the US Southwest.

Moore and Legner 1973(2) state of the genus that the male's head is, "above the antennal insertions, often with a forward directed horn on each side, which differs greatly in amount of development among the individuals". This identifies our specimen as male. One interesting feature is that the other pair of cephallic horns below these are curved inward and very much resemble oversized mandibles. Speculating, this may deter rodents from eating it, so may be a form of mimicry. The actual mandibles are much smaller and visible in the ventral and ventral head perspective views.

Note that a very small phoretic mite can be seen attached to the pronotum on the right. Detailed views of this sort of mite that I found on other beetles in the area that live in pine detritus and under bark, are shown here:



This image is derived from a stack of 72 images with a 28 µm step taken with a Nikon CF N Plan 4X/0.13 160/0 mm Achromat microscope objective + adapter/extension tube + Nikon D300 camera, and processed with CombineZP software.

Images of this individual: tag all
Siagonium punctatum male, dorsal - Siagonium punctatum - male Siagonium punctatum male, lateral - Siagonium punctatum - male Siagonium punctatum male, ventral - Siagonium punctatum - male Siagonium punctatum male, pronotum - Siagonium punctatum - male Siagonium punctatum male,  ventral head perspective - Siagonium punctatum - male

nice!

 
seconded
Sweet pics!

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