Confidence: It's likely to be this, but I can't be certain.
Notes: Reise, H., Hutchinson, J.M.C., Schunack, S., Schlitt, B. (2011). "Deroceras panormitanum and congeners from Malta and Sicily, with a redescription of the widespread pest slug as Deroceras invadens n. sp.". Folia Malacologica 19 (4): 201–233.