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Photo#605719
Carabid #20 - Anisodactylus laetus

Carabid #20 - Anisodactylus laetus
Medford, (~25 miles east of Philadelphia, PA) Burlington County, New Jersey, USA
May 27, 2011
Size: 8.3mm
here's a higher mag view of the mentum, with this "projection" in the middle where a "tooth" is sometimes present (in other genera). Haven't yet had a chance to check other known Anisodactylus for a similar structure, but comments welcome :)

Nikon 10x/0.25 M Plan 210/- objective on about 160mm, so ~7x on APS-C sensor, cropped to about 75% here. Steps hand-cranked on an A-stand, ~25 image Zerene PMax stack. In full resolution, looks like some finer steps are warrented, but shows the basic mentum structure I was trying to show.

Images of this individual: tag all
Carabid #20 - Anisodactylus laetus Carabid #20 - Anisodactylus laetus Carabid #20 - Anisodactylus laetus

can't check my specimens right now
but a similar projection can be seen in your

 
sure thing
yes, seems like that one has a similar projection. And if there were any doubt about this one being in the correct genus, the A. sanctaecrucis that you cite is certainly correctly IDed and in Anisodactylus. But all this just makes the D&A key a bit less accurate (in my opinon). Using tooth or no tooth is fine, but they should at least mention this projection, for those of us looking too casually.

 
Anisodactylus is notably without mentum tooth
except for the distinct tooth seen in A. verticalis (possibly others?). Closely related Notiobia and a couple other harpaline genera are distinguished by having such a tooth.

In checking my two reference specimens of A. laetus, I see that the mentum anterior margin is straight across. What your photo captured as a possible blunt "mentum tooth" is likely an unfortunate sculpturing of the ligula base. In my experience ligula vs mentum has been a frequent source of anatomic confusion which may only be resolved if the specimen is carefully checked in hand and under high magnification at various angles. A true mentum tooth is a smooth continuation and same coloration of the anterior margin of the mentum without evidence of a seam or interruption just below it.

This has been another good lesson in the pitfalls of photographic interpretation -- even with excellent quality images such as yours Tim.

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