Acochlidiacea

Source: Wikipedia, the free encyclopedia.

Acochlidiacea
Temporal range: Recent
↓
Acochlidium fijiiensis
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Mollusca
Class: Gastropoda
Subclass: Heterobranchia
Infraclass: Euthyneura
Superorder: Acochlidiacea
Odhner, 1937[1]
Families

(unranked)

Hedylopsacea

(unranked)

Microhedylacea

Diversity
46 species
Synonyms[2][3]

Acochlidiomorpha
Acochlidiida
Acochlidea
Acochlidia

Acochlidiacea, common name acochlidians, are a

mollusks within the large clade Heterobranchia
. Acochlidia is a variant spelling.

Schematic drawing of dorsal view of Pseudunela cornuta shows some characteristics of acochlidians, but characteristics of other acochlidians differ greatly:
f – foot
hb – heart bulb
lt – labial tentacle
rh – rhinophore
vh – visceral hump.

Description

These are mostly very small animals, without a

visceral mass being sharply set off from the rest of the body.[4]

Being a small group with only 47 species worldwide known in 2023,[5] this group has been the subject of active research since 2010, by which date only 32 species were named.[6] 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).[7] Most acochlidians live interstitially in marine sands, while some have conquered limnic systems (uniquely within opisthobranch gastropods).[7]

Taxonomy

Microhedylidae and Acochlidiidae.[1][2] In 1939, he treated this taxon as an order.[2][8]

Rankin (1979)[9] treated this taxon as an order, the order Acochlidioidea.[2][3]

Salvini-Plawen (1983)[10] wrote this taxon as Acochlidiomorpha.[3]

Anderson (1992)[11] treated this taxon as the order Acochlidiida.[2][3]

Burn in Beesley et al. (1998), wrote this taxon as the order Acochlidea.[3]

Wawra (1987)[12] and various authors (2007–2010)[7][13][14][15] spelled this taxon as Acochlidia.

Three families (

Microhedylidae and Acochlidiidae) are classically recognized.[2][3] Two controversial classifications (Rankin 1979,[9] Starobogatov 1983)[16] have been proposed recently, but they have not been evaluated since.[2][3]

An alternative classification by Burn (in Beesley et al., 1998) for the Australian species recognizes 2 superfamilies and 5 families.[2][3]

3D reconstructions like this one (Pseudunela cornuta) highly improved knowledge about acochlidians.

The Acochlidia, a traditional "order" of the Opisthobranchia since their establishment by Odhner have formed one of the unsolved mysteries within

parsimony analysis of morphological characters.[7] 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.[7]

Most recent morphological analyses suggested a common origin with either the equally enigmatic Rhodopemorpha, the diaphanid cephalaspidean Toledonia, or with runcinid or philinoid cephalaspideans.[7] 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).[7][17] 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.[7] However, only three derived acochlids were included into analysis prior to 2010, with partially missing data.[7]

2005 taxonomy

The taxonomy of Bouchet & Rocroi (2005)[2] tentatively follows Starobogatov (1983),[16] but they have downgraded his taxonomic ranks (suborders to superfamilies, superfamilies to families).[2][3] The group Acochlidiacea is arranged as follows:

  • Superfamily
    Acochlidioidea
  • Superfamily Hedylopsoidea
    • Family
      Hedylopsidae
    • Family
      Ganitidae
    • Family
      Livorniellidae
    • Family
      Minicheviellidae
    • Family Parhedylidae
    • Family
      Tantulidae
  • Superfamily
    Palliohedyloidea
    • Family
      Palliohedylidae
  • Superfamily Strubellioidea
    • Family
      Strubelliidae
    • Family
      Pseudunelidae

2010 taxonomy

A first comprehensive

phylogeny has been established by Schrödl & Neusser (2010),[15] but the identity of their sister group remained uncertain. Morphology-based analyses by Schrödl & Neusser,[15] demonstrated that Acochlidia usually group with other mesopsammic (they live in interstitial spaces of marine sands) taxa, if any were included (i.e. with the sacoglossan Platyhedyle, the rhodopemorph Rhodope or the cephalaspideans Philinoglossa or Philine exigua).[7] Thus, it is likely that convergent adaptations to the interstitial habitat mask the truly phylogenetic signals.[7]

Schrödl & Neusser (2010)[15] split Acochlidiacea into two (unranked) taxa and into six families like this:

Hedylopsacea

Hedylopsacean Acochlidiacea, whose evolution involves several habitat shifts from marine interstitial to amphibious or freshwater benthic habitats, possess complex excretory and reproductive systems.[18]

(unranked) Hedylopsacea has no superfamilies defined:[15]

Microhedylacea

Microhedylacean Acochlidiacea are exclusively found in interstitial spaces in sediment, and show a tendency toward reduction of complexity in major organ systems.[18]

(unranked) Microhedylacea has no superfamilies defined:[15]

  • Minicheviellidae
  • Paraganitus. Inclusion of Ganitidae within Microhedylidae requires further research and higher statistical support.[15]

A multi-locus molecular study by Jörger et al. (2010),

meiofaunal and brackish Pseudunelidae and limnic Acochlidiidae.[7] Inclusion of this small acochlidian group resulted in redefinition of major groups within Heterobranchia, that has led to creation of the new clades Euopisthobranchia and Panpulmonata.[7]

2016 taxonomy

Two more families were established. Both include slugs that are unusual among acochlidians for their anatomy and habitat (amphibious, terrestrial, or benthic in deeper waters):

Phylogeny

There is no fossil record of Acochlidiacea. Application of a

Microhedylacea.[7]

Cladogram

A cladogram showing phylogenetic relations of some genera and species within Acochlidiacea:[7]

Acochlidiacea

Ecology

The life cycle of Acochlidiacea is poorly known. With a typically low reproductive output in Acochlidiacea (max. of 40 eggs in Pontohedyle milaschewitchii), free veliger larvae are assumed to stay in the interstices of the sand grains rather than entering the water column thereby avoiding long distance dispersal.[18] Fertilized eggs are attached to sand grains and might promote dispersal via current driven sediment transport along shorelines.[18]

Overview of species

Acochlidium bayerfehlmanni
  1. Hedylopsis spiculifera (Kowalevsky, 1901) (Hedylopsidae) – marine
  2. Hedylopsis ballantinei Sommerfeldt & Schrödl, 2005 (Hedylopsidae) – marine
  3. Pseudunela cornuta (Challis, 1970) (Pseudunelidae) – marine and temporary brackish[6]
  4. Pseudunela eirene Wawra, 1988 (Pseudunelidae) – marine
  5. Pseudunela espiritusanta Neusser & Schrödl, 2009 (Pseudunelidae) – in brackish water
  6. Pseudunela marteli Neusser, Jörger & Schrödl, 2011 (Pseudunelidae) – marine[6]
  7. Pseudunela viatoris Neusser, Jörger & Schrödl, 2011 (Pseudunelidae) – marine[6]
  8. Aiteng ater Swennen & Buatip, 2009 (Aitengidae) – marine (and brackish)
  9. Aiteng marefugitus Kano, Neusser, Fukumori, Jörger & Schrödl, 2015 (Aitengidae) – marine
  10. Aiteng mysticus Neusser, Fukuda, Jörger, Kano & Schrödl, 2011 (Aitengidae) – from Japan[6][20]
  11. Bathyhedyle boucheti Neusser, Jörger, Lodde-Bensch, Strong & Schrödl, 2016 (Bathyhedylidae) - marine[19]
  12. Strubellia paradoxa (Strubell, 1892) (Acochlidiidae) – freshwater
  13. Strubellia wawrai Brenzinger, Neusser, Jörger & Schrödl, 2011 (Acochlidiidae) – freshwater
  14. Acochlidium amboinense (Strubell, 1892) (Acochlidiidae) – freshwater
  15. Acochlidium bayerfehlmanni Wawra, 1980 (Acochlidiidae) – freshwater
  16. Acochlidium fijiiensis Haynes & Kenchington, 1991[21] (Acochlidiidae) – freshwater
  17. Palliohedyle sutteri (Wawra, 1979) (Acochlidiidae) – freshwater
  18. Palliohedyle weberi (Bergh, 1895) (Acochlidiidae) – in brackish waters
  19. Tantulum elegans Rankin, 1979 (Tantulidae) – freshwater
  20. Asperspina brambelli (Swedmark, 1968) (Asperspinidae)
  21. Asperspina loricata (Swedmark, 1968) (Asperspinidae)
  22. Asperspina murmanica (Kudinskaya & Minichev, 1978) (Asperspinidae)
  23. Asperspina rhopalotecta Salvini-Plawen, 1973 (Asperspinidae)
  24. Asperspina riseri (Morse, 1976) (Asperspinidae)
  25. Microhedyle gerlachi Marcus & Marcus, 1959 - synonym: Parhedyle gerlachi (Ev. Marcus & Er. Marcus, 1959) (Microhedylidae)
  26. Microhedyle glandulifera (Kowalevsky, 1901) (Microhedylidae)
  27. Microhedyle nahantensis (Doe, 1974) (Microhedylidae)
  28. Microhedyle remanei (Er. Marcus, 1953) (Microhedylidae)
  29. Ganitus evelinae Marcus, 1953 (Microhedylidae s.l. / Ganitidae)
  30. Paraganitus ellynnae Challis, 1968 (Microhedylidae s.l. / Ganitidae)
  31. Parhedyle cryptophthalma (Westheide & Wawra, 1974) (Microhedylidae)
  32. Parhedyle odhneri (Ev. Marcus & Er. Marcus, 1955) - synonym: Microhedyle odhneri (Ev. Marcus & Er. Marcus, 1955) (Microhedylidae)
  33. Parhedyle tyrtowii (Kowalevsky, 1900) (Microhedylidae)
  34. Pontohedyle brasilensis (Rankin, 1979)[18] (Microhedylidae)
  35. Pontohedyle joni Jörger & Schrödl, 2013
  36. Pontohedyle kepii Jörger & Schrödl, 2013
  37. Pontohedyle liliae Jörger & Schrödl, 2013
  38. Pontohedyle martynovi Jörger & Schrödl, 2013
  39. Pontohedyle milaschewitchii (Kowalevsky, 1901) (Microhedylidae)
  40. Pontohedyle neridae Jörger & Schrödl, 2013
  41. Pontohedyle peteryalli Jörger & Schrödl, 2013
  42. Pontohedyle verrucosa (Challis, 1970) (Microhedylidae)
  43. Pontohedyle wenzli Jörger & Schrödl, 2013
  44. Pontohedyle wiggi Jörger & Schrödl, 2013
  45. Pontohedyle yurihookeri Jörger & Schrödl, 2013
  46. Helicohedyle dikiki Drainas, Carlson, Jörger, Schrödl & Neusser, 2017 (unassigned to family) – marine

References

This article incorporates CC-BY-2.0 text from references[7][18] and CC-BY-SA-3.0 text from the reference.[3]

  1. ^ a b (in German) Odhner N. H. (1937). "Hedylopsis suecica n.sp. und die Nacktschneckengruppe Acochlidiacea (Hedylacea)". Zoologischer Anzeiger 120(3–4): 51–64. 52, 62.
  2. ^
    ISSN 0076-2997
    .
  3. ^ a b c d e f g h i j Gofas, S. (2010). Acochlidiacea. In: Bouchet, P.; Gofas, S.; Rosenberg, G. (2010) World Marine Mollusca database. Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=411937 on 2010-11-30
  4. ISBN 0-03-056747-5
    .
  5. ^ MolluscaBase eds. (2021). MolluscaBase. Acochlidiimorpha. Accessed on 2023-02-13.
  6. ^
    doi:10.1371/journal.pone.0023313
    .
  7. ^
    doi:10.1186/1471-2148-10-323
    .
  8. ^ Odhner N. H. (1939). "Opisthobranchiate Mollusca from the western and northern coasts of Norway". Det Kongelige Norske Videnskabers Selskabs Skrifter 1939(1): 1–92. page 5.
  9. ^ a b Rankin J. J. (1979). "A freshwater shell-less mollusc from the Caribbean: structure, biotics, and contribution to a new understanding of the Acochlidioidea". Royal Ontario Museum, Life Sciences Contributions 116: 123 pp., page 83.
  10. ^ Salvini-Plawen L. v. (1983). Mollusca. In: Fauna & Flora des Mittelmeeres. Riedl R. (ed.) P. Parey. Hamburg & Berlin, 248–390. page 309.
  11. ^ Anderson C. (1992). Classification of organisms living and fossil. Golden Crown Press, Lancaster, Ohio, 69 pp., page 37.
  12. ^ Wawra E. (1987). "Zur Anatomie einiger Acochlidia (Gastropoda, Opisthobranchia) mit einer vorläufigen Revision des Systems und einem Anhang über Platyhedylidae (Opisthobranchia, Ascoglossa)". PhD thesis. Universität Wien.
  13. ^ Neusser T. P., Jörger K. M. & Schrödl M. (2007). "Exploring cerebral features in Acochlidia (Gastropoda: Opisthobranchia)". Bonn. Zool. Beitr. 55: 301–310.
  14. doi:10.1007/s00227-009-1158-5
    .
  15. ^
    doi:10.1111/j.1096-3642.2009.00544.x
    .
  16. ^ a b (in Russian) Starobogatov Ya. I. (1983). "Sistema otriada Acochlidiiformes [System of the order Acochlidiiformes]." Vsesoiuznoe soveshchanie po izucheniiu molliuskov, Leningrad, 7: 30–32.
  17. doi:10.1093/mollus/eyi014
    .
  18. ^
    doi:10.1186/1471-2148-12-245
    .
  19. ^
    doi:10.7717/peerj.2738
    .
  20. doi:10.1093/mollus/eyr033
    .
  21. ^ Haynes A. & Kenchington W. (1991). "Acochlidium fijiiensis sp. nov. (Gastropoda: Opisthobranchia: Acochlidiacea) from Fiji". The Veliger 34(2): 166–171.

External links

Wikimedia Commons has media related to Acochlidiacea.
Wikispecies has information related to Acochlidiacea.
Retrieved from "https://en.wikipedia.org/w/index.php?title=Acochlidiacea&oldid=1162734205"