High in the mists that shroud Mount Kaputar, near Narrabri in north-western NSW, scientists have discovered a secret world.

By day it is an isolated pocket of snow gums, wrapped in straggling native vines.

But on rainy nights, it is the domain of giant, fluorescent pink slugs and carnivorous, cannibal land snails that roam the mountaintop in search of their vegetarian victims.

''It's just one of those magical places, especially when you are up there on a cool, misty morning,'' said Michael Murphy, a national parks ranger for 20 years, whose beat covers the mountain top.

''It's a tiny island of alpine forest, hundreds of kilometres away from anything else like it. The slugs, for example, are buried in the leaf mould during the day, but sometimes at night they come out in their hundreds and feed off the mould and moss on the trees. They are amazing, unreal-looking creatures.''

Locals had long reported seeing bizarre pink slugs after rainfall in the area, but it was only very recently that taxonomists confirmed the slugs, Triboniophorus aff. graeffei, as well as several of the snail species - which prey on other vegetarian land snails - were unique to the mountaintop.

They are a relic of the era when much of eastern Australia was damp rainforest, and probably would have long since vanished, if a volcano had not erupted at Mount Kaputar about 17 million years ago.

The result of that eruption is a high-altitude haven for invertebrates and plant species that have been isolated for millions of years, after Australia dried out and the rainforests receded.

Their heritage can be traced back to Gondwana - when Australia's landmass was connected to others in one vast continent - via relatives that survive in pockets of New Zealand, New Caledonia and South Africa.

But the Mount Kaputar creatures are genetically distinct, restricted to an area of about 10 kilometres by 10 kilometres on their own mountaintop.

The NSW Scientific Committee has been persuaded by evidence of the area's uniqueness, and has just made a preliminary determination to list the site as an ''endangered ecological community'' - granting it one of the highest level of protection from intrusion and development.

''These species have evolved from lowland ancestors and have been isolated in an otherwise snail-hostile environment as conditions began to dry,'' the committee's report said. As a result, they are ''acutely susceptible'' to human-induced climate change. Temperatures a degree or two higher would dry out their mountaintop.

''I'm a big believer in invertebrates,'' Mr Murphy said. ''People tend to focus on the cute and cuddly bird and mammal species like koalas. But these little behind-the-scenes invertebrates really drive whole ecosystems.''