[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] 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][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.

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).

[18] (unranked) Hedylopsacea has no superfamilies defined:[15] Microhedylacean Acochlidiacea are exclusively found in interstitial spaces in sediment, and show a tendency toward reduction of complexity in major organ systems.

[7] The enigmatic amphibious and insectivorous Aitengidae clusters within Acochlidiacea, as sister to meiofaunal and brackish Pseudunelidae and limnic Acochlidiidae.

Both include slugs that are unusual among acochlidians for their anatomy and habitat (amphibious, terrestrial, or benthic in deeper waters): There is no fossil record of Acochlidiacea.

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.