What is "pterotracheidae"

Pterotracheidae is a family of medium-sized to large floating sea snails, pelagic gastropod molluscs. They are in the superfamily Pterotracheoidea along with two other similar pelagic families, the Atlantidae and the Carinariidae.

These pelagic snails are not at all closely related to the pelagic heterobranch opistobranchs such as the sea angels and sea butterflies. They are in the clade Littorinimorpha, and as such they are related to such families as the tritons ( Ranellidae) and the tun shells ( Tonnidae), in the clade Caenogastropoda.

According to taxonomy of the Gastropoda by Bouchet & Rocroi (2005) the family Pterotracheidae has no subfamilies.