Unlike some slugs, European Arionidae have no keel on the back.[1] The caudal mucous pit is above the tip of the tail.[1] The respiratory pore (pneumostome) is in front of the midpoint of the mantle.[1] The body length is up to 250 mm.[1] The mantle covers only a part of the body and lies in the anterior part.[1]
The jaw is odontognathic,[1] which means it is transversally ribbed. Radular teeth include: central tricuspid, lateral bi- or tricuspid, marginal bicuspid, all having broad bases.[1] Teeth are often accreted.[1] The digestive system forms 2 loops.[1] The heart, in relation to body axis, is titled to the left.[1] The kidney is circular (surrounding aorta).[1] Cephalic retractors tend to divide into separate branches attached independently to the posterior part of pallial complex.[1] The shell is strongly reduced in places, most often completely buried in the mantle, usually of loose crystals or plate-like.[1]Genitalia: the penis is present only in some species, epiphallus is present in nearly all of them.[1] Male copulatory organs are generally reduced, their role being taken over by a well-developed atrium and the epiphallus that produces spermatophores.[1]
In this family, the number of haploidchromosomes lies between 21 and 30 (according to the values in this table).[3]
^Barker G. M.: Gastropods on Land: Phylogeny, Diversity and Adaptive Morphology. in Barker G. M. (ed.): The biology of terrestrial molluscs. CABI Publishing, Oxon, UK, 2001, ISBN0-85199-318-4. 1-146, cited pages: 139 and 142. (In the reference specified as Ariononae.)
^Cockerell (1890). Ann. Mag. nat. Hist. (6)6: 278.
