Snails are found in almost all of New Zealand's waterbodies. They are so-called 'scrapers' feeding on bacterial, fungal and algal communities on leaf litter and rocks the with their tough rasping tongue ('radula'). As such, they are an important link between these less palatable forms of food and the larger animals; their typically large numbers providing an important food source for many other of the water body inhabitants e.g. koura and eels.
The main groups we have in New Zealand are the small introduced and more pollution tolerant and slow-water loving Physa species (illustrated), the native spiky-shelled Potamopyrgus species typical of faster-flowing waterbodies and the much larger growing introduced Lymnaea stagnalis from Europe.

Conservation status: As a result of their broad habitat and pollution tolerances freshwater snails are not endangered. However, even these tough little grazers may be lost from waterways if pollution if severe enough.

New Zealand's freshwater clams (also known as 'finger-nail clams' and 'pea mussels') are found around the country, in a variety of habitats, although they prefer silty bottomed waterbodies into which they can burrow.
Unlike the similar-looking freshwater mussels which only filter-feed, freshwater clams also directly ingest their food with their 'foot' from the surface of the bottom of the waterbody and from eating the sediment itself. Different again, their young are produced as perfect minitures of the adults, which no egg laying or plankton stage.

Conservation status: Clams are unlikely to be threatened and may even occur in higher numbers within waterbodies slightly increased nutrient runoff.

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These black limpets are less than 10 mm long, and are usually found clinging tightly onto relatively silt-free rocks and cobbles in streams and rivers. Here they feed, like most gastropods (snails), upon the surface films covering these rocks consisting of algae, bacteria and fungus. Little is known about the biology of these animals, including why they excrete a luminous green substance when disturbed e.g. by lifting them from their grip on a rock. This is possibly to deter potential predators. The only other freshwater animals that do this is are the freshwater glow-worms.

Conservation status: Freshwater limpets are not endangered, although they are relatively sensitive to pollutions and disturbances such as siltation of the cobbles and rocks in their habitats.