superorder of molluscs
|Four examples of Heterobranchia|
J.E. Gray, 1840
Heterobranchia is one of the main clades of gastropods. It has three informal groups:  The details are extremely complicated, and not yet quite worked out. Experts say they have "poorly resolved phylogenetic relationships".
- Lower Heterobranchia: a group of rather specialized, highly evolved sea slugs and sea snails.
- Opisthobranchia: almost all are marine species, some shelled and some not. They are a group of slugs and snails with grinding gizzard plates.
- Pulmonata. This is a group which is familiar to most people. It includes most land snails and slugs, many freshwater snails and a few marine species. They breathe air, are hermaphrodite, and usually have no operculum.
- Bouchet P. & Rocroi J.-P. (eds) 2005. Classification and nomenclator of gastropod families. Malacologia: International Journal of Malacology. 47(1-2). 
- Dinapoli A. & Klussmann-Kolb A. 2010. The long way to diversity – phylogeny and evolution of the Heterobranchia (Mollusca: Gastropoda). Molecular Phylogenetics and Evolution 55 (1): 60–76. 
- The operculum is the hard section on the foot which closes up the shell so the animal is safe inside.