| Planorbis Temporal range: Jurassic–recent |
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| Drawing of a shell of Planorbis planorbis | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Mollusca |
| Class: | Gastropoda |
| (unranked): | clade Heterobranchia clade Euthyneura clade Panpulmonata clade Hygrophila |
| Superfamily: | Planorboidea |
| Family: | Planorbidae |
| Subfamily: | Planorbinae |
| Tribe: | Planorbini[1] |
| Genus: | Planorbis O. F. Müller, 1774[2] |
| Species | |
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See text. |
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Planorbis is a genus of freshwater air-breathing snails, aquatic pulmonate gastropod mollusks in the family Planorbidae, the ram's horn snails, or planorbids. All species in this genus have sinistral or left-coiling shells.
Contents |
Planorbis shells are hard to make sense of in terms of their coiling and orientation. Most of the shells in this genus are almost planispiral in coiling, which means that the shell is coiled more or less flat. When examining the shell or the living animal, it is important to bear in mind the fact that planorbids have sinistral shells.
Once it is understood that a planorbid shell is sinistral, if the shell is held with the aperture on the left and facing the observer, then the sunken spire side of the shell is uppermost.
To repeat: the side of the shell which is in fact the spire (a sunken spire) faces downwards in the living animal, contrary to what is the case in almost all other shelled gastropods.
Worldwide distribution.
The genus is known from the Jurassic to the recent periods.[3]
Species within the genus Planorbis include: