Thanks for your nice comment David! Invertebrates are the 95% of animals, so is logic that I have more photos of them than from vertebrates. For me, they are as beautiful as vertebrates are.
The name Spanish Slug is not the best that could be choosed, but that is what I found in Google after typing on the species. The name is probably applied better to Arion lusitanicus, an endemic species of western Iberian Peninsula, that during much time was thought to be the same species than Arion vulgaris (differenciating these slugs is really tricky). After that, if was discovered than Eastern populations (like this one in the Pyrenees mountains) was actually Arion vulgaris and not A. lusitanicus.
I found a large population of these slugs in a trip to the highest peak of Spain, where I saw also more interesting wildlife, from alpine accentors and alpine sparrows to endemic snails and moths.