Arion lusitanicus, common name Portuguese slug, is a species

Species

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

 of air-breathing land slug

Slug

Slug is a common name that is normally applied to any gastropod mollusc that lacks a shell, has a very reduced shell, or has a small internal shell...

, a terrestrial

Terrestrial animal

Terrestrial animals are animals that live predominantly or entirely on land , as compared with aquatic animals, which live predominantly or entirely in the water , or amphibians, which rely on a combination of aquatic and terrestrial habitats...

 pulmonate gastropod mollusk in the family Arionidae

Arionidae

Arionidae, common name the "roundback slugs" or "round back slugs" are a taxonomic family of air-breathing land slugs, terrestrial pulmonate gastropod mollusks in the superfamily Arionoidea.- Distribution :...

.

Description

It is a rather large slug of reddish brown colour.

The more well known Spanish slug

Spanish slug

The Spanish slug, scientific name Arion vulgaris, more commonly known in English-speaking countries under the incorrectly applied Latin name, Arion lusitanicus, is a species of air-breathing land slug, a terrestrial pulmonate gastropod mollusk in the family Arionidae, the roundback slugs.This is a...

 was for a time misidentified as Arion lusitanicus, but the two slugs are not very closely related, differing in internal anatomy, shape of spermatophore

Spermatophore

A spermatophore or sperm ampulla is a capsule or mass created by males of various animal species, containing spermatozoa and transferred in entirety to the female's ovipore during copulation...

 and number of chromosomes.