They are holoplanktonic opisthobranch gastropod molluscs in the clade Thecosomata.

The lateral and posterior foot lobes are joined as a ciliated proboscis that leads to the mouth, and the wings are united ventrally to form a single plate.

The group was originally referred to as the Pseudothecosomata Meisenheimer, 1905, although this name is invalid under the ICZN and thus is no longer recognized.

[1] Instead its three families are categorized within the superfamily Cymbulioidea, which is itself part of the clade Thecosomata.

The superfamily Cymbulioidea consists of three following families (according to the taxonomy of the Gastropoda by Bouchet & Rocroi, 2005):