An extremely rare species of sea slug has been detected for the first time on a remote beach on the West Coast.
The "gravel maggot", whose scientific name is Smeagol climoi (yes, it's named after The Lord of the Rings character), was detected after a monitoring trip to the Hautai Marine Reserve in late January.
Three scientists from the University of Canterbury's Marine Ecology Research Group and two Māhaki ki Taiao rangers made up the trip.
The marine reserve is 85km south of Haast and holds the title of the country's most remote mainland marine reserve.
A study area where the gravel maggot was found requires a helicopter trip in and out, otherwise it's a two-day walk from the nearest road end.
The gravel maggot was detected using eDNA, which involves passing a litre of seawater through a very fine filter.
The DNA fragments of plants and animals collected in the filter were then analysed by a lab in Wellington.
The gravel maggot was among about 500 different species detected, which ranged from bacteria to dolphins.
Gravel maggots live up to 30cm down under the gravel beach surface. It is likely they have a small role in recycling nutrients from beachcast kelp back into the ecosystems of the surrounding oceans.
"We were incredibly shocked and delighted that the results came back confirming the presence of Smeagol within the sample that was taken," Don Neale, a marine ranger for the West Coast, said.
The gravel maggot has previously only been found in two places in the country - a small beach on the south coast of Wellington and Kaikōura.
The Kaikōura gravel maggot is a genetically-distinct population.
Neale said it's not known if the population in the Hautai Marine Reserve is its own species or related to the ones in Wellington and Kaikōura, which are 750km and 950km away.
"To figure this out would be a pretty major undertaking," Neale said.
"We would need to go back in to Hautai and spend some time digging carefully around gravel or under boulders to see if we can find any live gravel maggots there."