Historical reference: Do not rely on this information. It is very old. About this collection
Thecosonlata, the order of Pteropoda (q.v.) which includes those members of this class in which the body is protected by a mantle fold and a shell. It includes three living families, of which the Hyaleidae is the best known; the two Palaeozoic families of Conularidae and Theciidae are included here, but it is doubtful whether these are really Pteropods.