Systellommatophora
Encyclopedia
The Systellommatophora (synonym Gymnomorpha) is a clade of primitive, air-breathing 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...

s according to the taxonomy of the Gastropoda (Bouchet & Rocroi, 2005)
Taxonomy of the Gastropoda (Bouchet & Rocroi, 2005)
The taxonomy of the Gastropoda as it was revised by Philippe Bouchet and Jean-Pierre Rocroi is currently the most up-to-date overall system for classifying gastropod mollusks...

. The Onchidioidea are primarily marine (except for five land-dwelling or freshwater species), whereas the Veronicelloidea are primarily terrestrial.

These are marine
Marine (ocean)
Marine is an umbrella term. As an adjective it is usually applicable to things relating to the sea or ocean, such as marine biology, marine ecology and marine geology...

 and 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 gastropods within the Heterobranchia
Heterobranchia
Heterobranchia, the heterobranchs or Euthyneura, is a taxonomic clade of snails and slugs, which includes species from the sea, the land and freshwater; marine, aquatic and terrestrial gastropod mollusks....

.

Anatomy

No species have shells as adults. They are distinguished by the location of the anus
Anus
The anus is an opening at the opposite end of an animal's digestive tract from the mouth. Its function is to control the expulsion of feces, unwanted semi-solid matter produced during digestion, which, depending on the type of animal, may be one or more of: matter which the animal cannot digest,...

 at the rear of the body.

Neither superfamily bears shells as adults, although the Onchidioidea bear a vestigal, non-mineralized shell sac and possess a larval shell
Protoconch
A protoconch is an embryonic or larval shell of some classes of molluscs, e.g., the initial chamber of an ammonite or the larval shell of a gastropod...

. 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)
Taxonomy of the Gastropoda (Ponder & Lindberg, 1997)
The taxonomy of the Gastropoda, as revised by Winston Ponder and David R. Lindberg in 1997, is an older taxonomy of the class Gastropoda, the class of molluscs consisting of all snails and slugs...

 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)
Taxonomy of the Gastropoda (Bouchet & Rocroi, 2005)
The taxonomy of the Gastropoda as it was revised by Philippe Bouchet and Jean-Pierre Rocroi is currently the most up-to-date overall system for classifying gastropod mollusks...

:
  • superfamily Onchidioidea Rafinesque, 1815
    • Onchidiidae
      Onchidiidae
      Onchidiidae are a family of small, air-breathing sea slugs. They are shell-less marine pulmonate gastropod molluscs. Onchidiidae is the only family within the superfamily Onchidioidea....

       Rafinesque, 1815
  • Superfamily Veronicelloidea
    Veronicelloidea
    Veronicelloidea is a superfamily of air-breathing land slugs. They are terrestrial pulmonate gastropod molluscs.- Taxonomy :The following two families have been recognized in the taxonomy of Bouchet & Rocroi :* family Veronicellidae Gray, 1840...

     Gray, 1840
    • Veronicellidae
      Veronicellidae
      The Veronicellidae, common name the leatherleaf slugs, are a terrestrial family of pulmonate slugs.This family has no subfamilies ....

       Gray, 1840
    • Rathouisiidae
      Rathouisiidae
      Rathouisiidae is a family of air-breathing land slugs, terrestrial pulmonate gastropod mollusks.- Taxonomy :The Rathouisiidae family is classified in the clade Systellommatophora within the clade Eupulmonata...

      Heude, 1885
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