A diving expedition into a Nelson cave, one of the world's deepest, has uncovered three species Niwa says have never been seen before.

The National Institute for Water and Atmospheric Research (Niwa) is working to find names for the new species; a transparent crustacean, a gastropod snail and an oligochaete worm.

Found in the depths of the Pearse Resurgence - an underwater cave in the Mt Arthur Range near Nelson - a team of Australian divers who were mapping the cave made the discoveries and brought them back to Niwa.

There are 16 diveable caves in the world deeper than the Pearse Resurgence.

Only 10 of those have been dived to depths greater than the current depth explored in the Pearse (194 metres).

The divers camped on site for 13 days, making a total of 74 dives into 6.5 degree water.

Niwa scientist Graham Fenwick said the new species discovery was important for two reasons.

"They [the organisms] contribute to the health of the aquifer by biofiltration and, in turn, they may represent an important marker of the health of the water."

An aquifer, also known as a karst system, is an underground body of saturated rock through which water can easily move.

Fenwick said studies such as this were important as scientists worldwide were working to document the biodiversity of Earth.

"It's important to do an inventory of life in New Zealand, and in this case, it's a pretty special type of environment and we don't have many limestone karst systems that are readily explored."

It is expected to take up to 18 months while scientists study their morphology and body shape before the creatures are named.

The divers used two methods to collect the stygofauna - a word meaning animals from the River Styx.

In the first, divers captured any invertebrates observed free-swimming by using a stygoslurper.

The tube with a bulb on the end, similar to a turkey baster, would suck the invertebrates up along with water.

The second technique involved using small plastic jars baited with shrimp and filled with nylon gauze.

The jars were secured in various places in the cave and in crevices among the sediment, between five and 115 metres below the surface.

The amphipod crustacean they found was completely colourless.

"It is six to eight millimetres long, the divers could see it crawling over rocks - it really is a beautiful animal," Fenwick said.

"It belongs to the poorly-known genus paraleptamphopus, one of two genera within the New Zealand endemic family paraleptamphopidae."

That meant the species were native to New Zealand, and most likely endemic to that particular area.

Within the Pearse Resurgence, the creature was found mainly inside the main shaft at depths between two and 40 metres.

The other two invertebrates were taken from rare deposits of sediment within the main shaft between 15 and 34 metres deep.

- © Fairfax NZ News

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