The Systellommatophora (synonym Gymnomorpha) is a clade of primitive, air-breathing slugs, according to the taxonomy of the Gastropoda (Bouchet & Rocroi, 2005). 
|Land slug Laevicaulis alte (Veronicelloidea)|
|Sea slug Onchidella sp. (Onchidioidea)|
They are marine and terrestrial pulmonate gastropods within the Heterobranchia. There are two superfamilies in this clade. Slugs in the superfamily Onchidioidea are primarily marine (except for five land-dwelling or freshwater species), whereas slugs in the superfamily Veronicelloidea are primarily terrestrial.
Although neither superfamily bears shells as adults, the Onchidioidea do possess a vestigial, non-mineralized shell sac and possess a larval shell. It is not known whether or not the veronicellids bear a larval shell.
According to the previous taxonomy of the Gastropoda (Ponder & Lindberg, 1997) Systellommatophora was considered to be a suborder or an order.
The following two superfamilies and families have been recognized in the taxonomy of Bouchet & Rocroi (2005):