The Systellommatophora (synonym Gymnomorpha) is a clade of primitive, air-breathing slugs, according to the taxonomy of the Gastropoda (Bouchet & Rocroi, 2005).MolluscaBase eds. (2020). MolluscaBase. Stylommatophora. Accessed through: World Register of Marine Species at: http://www.marinespecies.org/aphia.php?p=taxdetails&id=447 on 2020-05-02
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.
Anatomy No species in this clade has a shell as an adult. These slugs are distinguished by the location of the anus at the rear of the body.
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.
Taxonomy 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): superfamily Onchidioidea Rafinesque, 1815 Onchidiidae Rafinesque, 1815 Superfamily Veronicelloidea Gray, 1840 Veronicellidae Gray, 1840 Rathouisiidae Heude, 1885
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