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Guide to New Zealand's freshwater invertebrates
Planorbella is an introduced snail with a thin and fragile shell that looks as though the spire (or pointed end) has been chopped off. There is no operculum (protective shield) covering the aperture (shell opening) when the animal withdraws. The aperture is on the left when facing toward you and when the spire (in this case the flat plane where the spire should be) faces upwards (see lower photo).
Planorbella is probably common in aquaria, ponds and some lakes. We have found it to be common in some parts of the Waikato River.
Like most snails they are grazers, scraping biofilms from submerged surfaces.
The presence of Planorbella in the Waikato River may be the result of populations in the Waikato hydroelectric lakes that support large beds of introduced oxygen weeds (possibly ideal habitats for this exotic snail). They have not been assigned any tolerance values.