Pharynx (as one of frontal parts of the digestive system of gastropods) in number of carnivourous gastropods can be everted to draw the prey easily into the predator’s body.
Arion vulgaris is omnivorous and it is not known to evert its pharynx during feeding (as far as I know). This photo of Arion vulgaris shows the dead or nearly dead specimen with buccal mass everted out of the body . I am not sure what exactly has stimulated to this specimen to evert its pharynx, but I think that it was caused by some deadly conditions such as drowning in water with mucus.
The buccal mass consist of mouth and buccal cavity (=pharynx). Mouth has lips. There are visible lips on the the photo (the left part of the white extended part). Behind the lips there is oral tube (not visible on this photo) leading to the buccal cavity (=pharynx, the right part of the white extended part). Inside the buccal cavity there is the jaw, the radula sac containing the cartilaginous odontophore and the radula on the odontophore (all of them are hidden inside the pharynx). The radula sac can be seen on the posterior part of the buccal cavity (on the top righ of this photo), but I do not know exactly how much is the radula sac extended into the buccal cavity.
The head of this slug is dirty dark brown in color. I think, that there is also visible frontal part of the oesophagus, that starts normally on the dorsal part of the buccal mass. Oesophagus is visible in light brown-reddish color before the frontal part of the head.
The slug has also two ducts from salivary glands leading to the buccal mass. They are on sides of the oesophagus, but they are not visible on the photo and I have not find these ducts on this specimen. There should be also buccal retractor, but I was unable to identify that muscle also.
This photo shows main parts of the digestive system of gastropods, that are responsible for reception of the food.