Great Black Slug

I've moved this slug from the Arthropod category to the Other category for you. Snails and slugs are Mollusks. Arthropods have an exoskeleton and jointed limbs in at least one phase of their life. Think dragonfly, bee, crab, and ant.

Thank you Lenny for that detailed information. Much appreciated

The dominant species is Arion ater.
There are tw subspecies Arion ater ater and Arion ater rufus.
There are no known hybrids.
There are ten color forms (cf)
cf. albida Whitish grey/white
cf. albolateralis Black with white or grey sides
cf. atra Black
cf. bicolor Brown with cream sides
cf. brunneofasciata Brown with pale sides
cf. castanea Dark brown
cf. plumbea Grey
cf. reticulata Pale with dark stripes
cf. rubra Red/brown
cf. succinea Orange

I would say that is more a red slug than a black one, Arion rufus...

This is a color form of Arion Ater.Possibly brunneofasciata or bicolor.
There are many color forms,10 I think.