Hybrid Slug?

I spotted this specimen several weeks ago, and at the time I believed it was Deroceras laeve, the Marsh Slug. After further examination of the photos, I think that's still the best hypothesis. It was simply strange to see this species so far from the house (it was up the hill in the area fenced by cross-ties). Usually they keep close by the porch. That being said, however, the characteristics of this slug are still different from that which I normally see in Deroceras laeve. Yes, the dark cephalic tentacles, mottled gray coloring, and smaller size all match up, but I've yet to see D. laeve with such a discernible mantle. Not that you can't see the mantle in this species--in fact it's quite long--but I've never observed it to contrast so distinctly with the body in terms of color: while the body is gray, the mantle is brown! The specimens that bear the closest similarity have only a patch of brown on their mantle, covering no more than half its area, usually less. Even so, the length and positioning of the mantle indicate that this specimen is most likely D. laeve. Yet apparently not all members of this species possess significant tubercles; some bodies appear quite smooth. (This also occurs in L. valentiana; merely superficial differences between individuals, just like the faintness or darkness of bands in L. valentiana).

Those are L. valentiana surrounding our subject.

Nevertheless, as with another specimen (#6), a fleeting thought crossed my mind that perhaps there could be hybrids of Deroceras laeve and Lehmannia valentiana (that the two species cross-breed across genera)...Particularly with specimen #6 mentioned in the link above, there is the faintest trace of black bands on the mantle, suggestive of L. valentiana's tell-tale lyre shape, but that's a pretty far-fetched conjecture right now. As D. laeve is so mottled anyway, it's difficult to determine if any marks are unusual. I'm going to keep my eyes peeled, though. If toads can become hybridized, why not slugs?