Deroceras panormitanumsensu stricto ("in the strict sense") occurs predominantly only on Sicily and Malta.[2] Before 2011,[3] this name was also applied to what turned out to be a distinct species, Deroceras invadens, a species which has spread around the world and is often a pest.
Deroceras panormitanum was described from Palermo in Sicily.[1] It is now widely accepted[3][5][6] that Deroceras pollonerae also described from Palermo,[7]Deroceras caruanae described from Valletta on Malta,[8] and Deroceras dubium from Malta[9] are the same species. Recently Reise et al. (2011)[3] also synonymised Deroceras giustianum from NW Sicily[10] but considered the status of further similar taxa from this general region as uncertain. Now that Deroceras invadens has been recognised as distinct, the morphological variation within Deroceras panormitanum sensu stricto is not as great as once thought.
Description
The skin and flesh of Deroceras panormitanum is watery and fairly transparent. The skin colour varies between pale grey, brown, and black. The mucus is colourless. Externally, Deroceras panormitanum is impossible to distinguish from Deroceras invadens and Deroceras golcheri, which occur in the same islands, and from a variety of other Deroceras species occurring elsewhere.[3][6]
Internally the penis of Deroceras panormitanum has two side pockets (penial caecum and penial lobe), as in Deroceras invadens but unlike in Deroceras golcheri or related forms on Sicily.[3] In Deroceras panormitanum the caecum is more tapering and pointed than in Deroceras invadens. Whereas in Deroceras invadens the retractor muscle attaches directly to a point on the penis between the caecum and lobe, in Deroceras panormitanum it attaches first to the lobe. Also the penial glands often appear more knobbly than in Deroceras invadens. And inside the penis, between the distal and proximal parts, is a small flap that is absent in other species.
Reise et al. (2011)[3] detail the mating behaviour and compare it with that of Deroceras invadens and Deroceras golcheri.
^Pollonera, C. (1891). "Appunti di malacologia. VII. Intorno ai Limacidi di Malta". Bollettino dei Musei di Zoologia ed Anatomia Comparata della Reale Università di Torino. 6: 1–4.
^Wiktor, A. (1998). "Two new for science Deroceras species from France and the Italian island of Sicily (Gastropoda: Pulmonata: Agriolimacidae)". Malak. Abh. 19: 13–19.
^Giusti, F.; Manganelli, G.; Schembri, P.J. (1995). The non-marine molluscs of the Maltese Islands. Monografie XV, Museo Regionale di Scienze Naturali, Torino.
^Rowson, B.; Anderson, R.; Allen, S. (2016). "Another wave of invasion? First record of the true Sicilian slug Deroceras panormitanum sensu stricto from Ireland, and another from Wales (Pulmonata: Agriolimacidae)". Journal of Conchology. 42 (3): 123–125.
^Castillejo, J.; Iglesias, J. (2017). "Las babosas de las Islas Baleares (Gastropoda: Pulmonata: Testacellidae, Milacidae, Agriolimacidae, Limaidae y Arionidae)". Spira. 6: 97–127.