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Guide to New Zealand's freshwater invertebrates
Halopyrgus (formerly Potamopyrgus) pupoides is a small brown snail related to the more common Potamopyrgus. The shell has an obvious spire, but the apex is somewhat rounded, and there is little definition between the whorls, giving the shell a relatively smooth outline. There is an operculum (protective shield) covering the aperture (shell opening) when the animal withdraws. The aperture is on the right when facing toward you and when the spire points upwards.
Our records of Halopyrgus are from the upper estuarine reaches of streams and rivers where there is some seawater intrusion.
Like most snails they are grazers, scraping biofilms from submerged surfaces.
The presence of Halopyrgus is likely to indicate salinity due to sea water intrusion. We don’t know enough about their other habitat and water quality requirements to assign tolerance values.