'New' swimming cave cricket species filmed
A swimming cricket was one of three possible "new species" filmed by a TV crew working in South America.
The "unbelievable" insect find was captured on camera along with a no-eyed harvestman and a cave catfish.
The trio were found in a cave system of a remote Venezuelan tepui, a type of table-top mountain in the region.
The three creatures have not been formally described but members of the team believe that they are new species.
"We've only named about a million species of insects and there are almost certainly five to eight million undescribed," said biologist and presenter, Dr George McGavin.
The filming was part of a new BBC/Discovery Channel/Terra Mater TV co-production called The Dark: Nature's Nighttime World.
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"[It's] the most unbelievable thing I've ever seen," Dr McGavin, told BBC Nature.
"It swims underwater and uses its front legs as a proper breaststroke and its hind legs kicking out. It was just amazing," he said.
The team were alerted to the cave by Italian researchers from the association La Venta, who had noted the presence of an unusual looking catfish when they recently explored the caves.
Dr McGavin and the film crew went with them during their return trip to the cave and found a specimen with the hallmarks of an underground evolutionary history.
With a pale colour and only remnants of eyes, its pitch black habitat seemed to have negated any need for visual communication or sight.
The fish navigated using large sensitive organs on the front of its head.
It is thought that millions of years ago the catfish's ancestors must have lived in water on the plain from which the cave was formed.
"What was originally a catfish perhaps in a lake, suddenly becomes an isolated catfish in these hidden underground areas," said Dr McGavin.
In the same three-mile stretch of cave, he also discovered a harvestman which he believes is new to science:
"(It) was just such a weird animal and I haven't seen a picture or a drawing of anything that looks even vaguely similar, so I'm reckoning that it is undescribed."
Find out more
The Dark: Nature's Nighttime World continues on BBC Two in the UK at 21:00 BST on Sunday 5 August and elsewhere at a future date.
Harvestmen are arachnids, a group of animals that includes spiders and scorpions but this one was unusual as it did not react to Dr McGavin's torchlight.
On closer inspection, the team realised the reason for this was that the harvestman had no eyes.
"If we'd had the time there would have been other [discoveries] there," said Dr McGavin.
"You can't really as a biologist, put into words how it feels to see something, to film something that's never been named."
Although the trio have not yet been formally described, there is a high chance that all three are new species due to their remote location.
"Caves tend to be very isolated so when some adventurous... organism finds its way into the cave, the populations there typically do not come into contact with populations in other caves or the above-ground ancestors that they came from," explained Professor Quentin Wheeler, director of the International Institute for Species Exploration at Arizona State University.
Top Ten new species 2012
"Anytime that you get small in-breeding populations, you can have speciation occur far more rapidly than large populations that are interbreeding with more regularity."
Conservation biologists call places like this hotspots - areas inhabited by a high number of endemic species that cannot be found anywhere else.
"Places like small islands and mountain tops and caves are really new exciting laboratories of genetic experimentation," said Professor Wheeler.
The International Institute for Species Exploration collates information about newly discovered species, in part because of its value in the study of evolutionary history but also out of a concern for bio-diversity and conservation.
They record around 18,000 new species a year but Professor Wheeler said that they are not about to run out of discoveries.
"We know that about two million species have been named and described but we think there are at least in the order of 10 million additional species," he said.
"That's only counting multi-cellular plants and animals, if we get into the microbial world it's a whole different ball game."
Every year, the institute publishes a top ten of the past year's newly discovered species. Professor Wheeler picked out the Devil's worm as his highlight from last year's list.
"It was found nearly a mile beneath the surface and I don't think anyone expected to find a relatively large multi-cellular organism living that deep.
"To me it just says, 'Well what else don't we know?'"
The Dark: Nature's Nighttime World is a BBC/Discovery Channel/Terra Mater co-production and continues on BBC Two at 21:00 BST on Sunday 5 August and elsewhere at a future date.