Guide to New Zealand's freshwater invertebrates

Snail ( Planorbidae : Glyptophysa )

Nodules and shouldering on whorls

Diagnostic features

Glyptophysa (formerly Physastra) is a native snail genus that appears to have become increasingly rare over recent decades. They are similar in shape to the introduced Physa, but Glyptophysa has rings of nodules or shouldering around the edges of some whorls. As with Physa there is no operculum (protective shield) covering the aperture (shell opening) when the animal withdraws, and the aperture is on the left when facing toward you and when the spire points upwards (see lower photo).

Typical habitats

Glyptophysa tend to be found in wetlands or slow flowing streams amongst aquatic plants.

Feeding

Like most snails they are grazers, scraping biofilms from submerged surfaces.

Indicator value

The presence of Glyptophysa is probably of more conservation interest than water quality interest. They have been assigned tolerance values of 5 (hard bottom sites) and 0.3 (soft bottom sites).