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Guide to New Zealand's freshwater invertebrates
Ferrissia (synonym Gundlachia) are small, limpet-shaped snails, often with semi-transparrent shells that are easily overlooked (if you don’t have a microscope). Small individuals have fragile shells, but with increasing size the shells become more thickened and coloured. The limpet shape is asymetrical but not as paua-shaped as the larger native limpet Latia.
Ferrissia are most common in slow-flowing, weedy streams where they often attach to submerged plant surfaces. Some populations also occur on stony bottom streams.
Like most snails they are grazers, scraping biofilms from submerged surfaces.
Ferrissia can be abundant in farmland streams with moderate to poor water quality. They have been assigned tolerance values of 3 (hard bottom sites) and 2.4 (soft bottom sites).