Hedylopsacea
| Acochlidiacea Temporal range: Recent |
|
|---|---|
 |
|
| Acochlidium fijiiensis | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Mollusca |
| Class: | Gastropoda |
| (unranked): |
clade Heterobranchia clade Euthyneura clade Panpulmonata clade Acochlidiacea Odhner, 1937 |
| Families | |
|
(unranked) Hedylopsacea (unranked) Microhedylacea |
|
| Diversity | |
| 33 species + 9 undescribed in 2012 | |
| Synonyms | |
|
Acochlidiomorpha |
|
(unranked) Hedylopsacea
(unranked) Microhedylacea
Acochlidiomorpha
Acochlidiida
Acochlidea
Acochlidia
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.
These are mostly very small animals, without a shell or gills, distinguished by the visceral mass being sharply set off from the rest of the body.
Being a small group with only 30 species worldwide known in 2010, and 32 species described in 2011, and 33 in 2012 (+9 undescribed Pontohedyle species), these slugs are morphologically and biologically highly aberrant and diverse, comprising a series of unusual characters (e.g. secondary gonochorism, lack of copulatory organs, asymmetric radulae). Most acochlidians live interstitially in marine sands, while some have conquered limnic systems (uniquely within opisthobranch gastropods).
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.
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Wikipedia