| Planorbella | |
|---|---|
| Planorbella trivolvis | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Mollusca |
| Class: | Gastropoda |
| (unranked): | clade Heterobranchia clade Euthyneura clade Panpulmonata clade Hygrophila |
| Superfamily: | Planorboidea |
| Family: | Planorbidae |
| Genus: | Planorbella Haldeman, 1843[1] |
Planorbella is a genus of freshwater air-breathing snails, aquatic pulmonate gastropod mollusks in the family Planorbidae, the ram's horn snails, or planorbids, which all have sinistral, or left-coiling, shells.
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Planorbid gastropod shells are hard to make sense of in terms of their coiling and orientation. Most of the shells in this family are almost planispiral in coiling, and it is important to bear in mind the fact that all planorbids have sinistral shells. To complicate matters further however:
The planorbid shell is sinistral, such that one can hold the shell with the aperture on the left and facing the holder; then the sunken spire side of the shell will be uppermost. That is to say: the side of the shell which is in fact the spire (a sunken spire) often is carried facing down in the living animal, contrary to what is the case in almost all other shelled gastropods.
Species in the Planorbella genus are sometimes hosts for parasites, constituting a link in the pathway of infection for higher animals. For example, some species of Planorbella host rediae and cercariae stages of the parasite Ribeiroia, prior to ultimate infection of the Rough-skinned Newt.[2]
Planorbella are often algae grazers, and in some locations such as oligotrophic sloughs, they may be a dominant element of total ecosystem biomass and hence system integrity.[3]
Species within the genus Planorbella include: