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Photo#616934
Drassyllus Eye Arrangement - Drassyllus

Drassyllus Eye Arrangement - Drassyllus

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I think that sometimes the PME in this genus can be more rounded (the lens), as in this adult male Drassyllus niger (the tapetum inside the eyes of this species do seem to point together toward the rear, though):


In Gnaphosidae of the World (2007), by John Murphy, the PME are shown as rounded for this genus in the eye diagram of the representative species he uses (Vol 2, page 212, Drassyllus fallens).

I'm just not sure that posteriorly-converging PME are a diagnostic feature for this genus.

 
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But see page 108 in SONA: "PME usually oval, larger than PLE, closely spaced; PER slightly procurved (Fig. 29.18)." This is in the couplet that takes you to Camillina (Florida, Alabama) and Drassyllus. In Paquin & Dupérré 2003 it (although I can only see the figures and can't read the descriptions) separates Zelotes and Drassyllus.

Perhaps this only can be applied to (some/most?) North American species? Looking at some of the images I have of a few species, this characteristic seems to hold -- the actual shape of the AMEs does vary somewhat, but they do all seem to come pretty close together.

Here is what I have in my notes (unfortunately without attribution -- could be Lissner): "Posterior medial eyes larger than laterals and in most species oval and oblique."

 
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In Dondale and Platnick (1992), the PME eyes are shown as more rounded than in your specimen (but not fully round) - see diagram 8 on p. 13. In their genus key, Drassyllus and Urozelotes both have "Posterior median eyes distinctly larger than posterior lateral eyes and separated by less than half their maximum width." But, the authors say nothing specific about the shape, or that they are necessarily pointing toward the rear. The two genera are then separated by the genetalia.

Regarding Canadian gnaphosids, Dondale and Platnick write that, "Members of the genus Drassyllus are distinguished from those of other Canadian gnaphosid genera by the [...] nearly touching posterior median eyes [...]" (p. 99). They say nothing about the shape of the eyes. Based on that and the variable shape of the PME, I'd argue that oval eyes that point convergently and posteriorly, as in your specimen above, are not a diagnostic feature, since that feature is not present in all Drassyllus spp.

That is, I agree with you on that the PME being larger than PLE and close together is a diagnostic feature, but not the shape of the PME, which varies within the genus.

 
Perhaps
we should try this as one of our field markings and see if it always pans out? It seems like an easy way to separate the black Drassyllus from Zelotes to me. From what I can see in the guide it seems to be reliable. The male image shown above shows the same pointed eyes as Kevin's image does. Perhaps we just need to add a disclaimer of some sort?

 
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I'm going to do some more reading on the genus and see what turns up.

 
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