Acochlidiimorpha

This is a small group of Heterobranchs comprising about 30 species worldwide and living in the interstitial marine or freshwater medium. They have been very poorly studied, they are very small and have a somewhat aberrant body morphology for being molluscs. They have adapted to live and move between the sediment particles.

Acochlidium fijiiensis Haynes & Kenchington, 1991
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They have an elongated body, with no shell when adults, and a mantle that usually has numerous spicules. They have no gills nor mantle cavity and the head has oral tentacles and rhinophores. Generally the sexes are separated. They possibly feed on microorganisms that live in the interstitial medium.

Traditionally considered a peculiar group of opisthobranchs, recent works by Jorger et al. (2010) and Schrödl et al. (2011) tend to classify them closer to pulmonate gastropods within the clade Panpulmonata.

The taxonomy of Acochlidiimorpha according to recent work by Bouchet et al. (2017) is:

• Superorder Acochlidiimorpha
  • Superfamily Acochlidioidea Küthe, 1935
    • Family Acochlidiidae Küthe, 1935
      • Genus Acochlidium Strubell, 1892
      • Genus Palliohedyla Rankin, 1979
      • Genus Palliohedyle Rankin, 1979
      • Genus Strubellia Odhner, 1937
    • Family Aitengidae Swennen & Buatip, 2009
      • Genus Aiteng Swennen & Buatip, 2009
    • Family Bathyhedylidae Neusser, Jörger, Lodde-Bensch, Strong & Schrödl, 2016
      • Genus Bathyhedyle Neusser, Jörger, Lodde-Bensch, Strong & Schrödl, 2016
    • Family Hedylopsidae Odhner, 1952
      • Genus Hedylopsis Thiele, 1931
    • Family Pseudunelidae Rankin, 1979
      • Genus Pseudunela Salvini-Plawen, 1973
    • Family Tantulidae Rankin, 1979
      • Genus Tantulum Rankin, 1979
  • Superfamily Parhedyloidea Thiele, 1931
    • Family Asperspinidae Rankin, 1979
      • Genus Asperspina Rankin, 1979
      • Genus Minicheviella Starobogatov, 1983
    • Family Parhedylidae Thiele, 1931
      • Genus Microhedyle Hertling, 1930
      • Genus Parhedyle Thiele, 1931
      • Genus Pontohedyle Golikov & Starobogatov, 1972

In the Mediterranean and around the Iberian Peninsula the following species have been reported:

Asperspina loricata	Hedylopsis spiculifera
Microhedyle glandulifera	Pontohedyle milaschewitchii

So far no Acochlidiacea has been cited in the Catalan coast, because of the lack of studies of the interstitial medium directed towards this group.

Bibliography

1246567 Acochlidiimorpha items 1 entomological-society-of-america author asc 1 https://opistobranquis.info/wp-content/plugins/zotpress/
Bibliography based on the works by Steve Long, 2006. Bibliography of Opisthobranchia 1554-2000 and Gary McDonald, 2009. Bibliographia Nudibranchia, with later updates from other resources.