page_title: Acochlidiacea
section_title: Taxonomy
hierarchical_section_title: Acochlidiacea / Taxonomy
caption_attribution_description: English: 3D reconstruction of the general anatomy of the right view of small marine slug Pseudunela cornuta. It is a 3D model generated from 420 histological sections by segmentation and surface extraction. - The histological sections have been aligned and stacked together to form a 3D volume, which was then segmented. For each segment mathematical representation of its surface was generated (boundary surface extraction) and then this 3D model was visualized by rendering the surfaces.
context_page_description: Acochlidiacea, common name acochlidians, are a taxonomic clade of very unusual sea snails and sea and freshwater slugs, aquatic gastropod mollusks within the large clade Heterobranchia. Acochlidia is a variant spelling.
context_section_description: Nils Hjalmar Odhner established this taxon as a family in 1937, when he created the families Microhedylidae and Acochlidiidae. In 1939, he treated this taxon as an order.
  Rankin (1979) treated this taxon as an order, the order Acochlidioidea.
  Salvini-Plawen (1983) wrote this taxon as Acochlidiomorpha.
  Anderson (1992) treated this taxon as the order Acochlidiida.
  Burn in Beesley et al. (1998), wrote this taxon as the order Acochlidea.
  Wawra (1987) and various authors (2007–2010) spelled this taxon as Acochlidia.
  Three families (Hedylopsidae, Microhedylidae and Acochlidiidae) are classically recognized. Two controversial classifications (Rankin 1979, Starobogatov 1983) have been proposed recently, but they have not been evaluated since.
  An alternative classification by Burn (in Beesley et al., 1998) for the Australian species recognizes 2 superfamilies and 5 families.
  The Acochlidia, a traditional "order" of the Opisthobranchia since their establishment by Odhner have formed one of the unsolved mysteries within Euthyneura. Their monophyly is widely accepted especially since a proposed sister group relationship of the acochlidian family Ganitidae with Sacoglossa (based on the dagger-shaped radula teeth) could be rejected based on a comprehensive parsimony analysis of morphological characters. During the last years a series of studies have redescribed key acochlidian taxa in great detail, including 3D reconstructions, and added considerably to the morphological and biological knowledge of this previously little understood group.
  Most recent morphological analyses suggested a common origin with either the equally enigmatic Rhodopemorpha, the diaphanid cephalaspidean Toledonia, or with runcinid or philinoid cephalaspideans. Molecular markers independent from direct ecological pressures suggested an unresolved basal opisthobranch origin for Acochlidia (based on nuclear 18S rRNA and 28S rRNA) (Vonnemann et al. 2005). A first combined multi-gene dataset led to the surprising result of Acochlidia clustering in a pulmonate relationship, united in a clade with Pyramidelloidea, Amphiboloidea and Eupulmonata. However, only three derived acochlids were included into analysis prior to 2010, with partially missing data.
caption: 3D reconstructions like this one (Pseudunela cornuta) highly improved knowledge about acochlidians.
exif: {"Thumbnail JPEGInterchangeFormat": "44", "Thumbnail JPEGInterchangeFormatLength": "9352"}