A strange green slime discovered by researchers in Australia has been claimed to represent an "unknown" form of life.
The 'curtains' of green matter have been found deep beneath water-filled underground caves in the country's Nullarbor Plain.
The biological material - nicknamed 'Alien Slime' - is extremely unusual and unlike anything found elsewhere on the planet, the team said.
The researchers from Macquarie University said in their report, published this week in the International Society For Microbial Ecology journal, that the slimes thrive in total dark, independent of the Sun.
"Earlier studies on the community suggested that there was an unusual chemistry going on in the caves, but we didn't know how the microbes were making a living in the cave environment," said lead scientist Professor Ian Paulsen.
Investigations showed that a dominant group of organisms - Thaumarchaeota - were effectively in control, and might have marine origins.
It is supposed the cave was regularly flooded by sea water, and that the Thaumarchaeota evolved during periods of isolation.
"It just goes to show that life in the dark recesses of the planet comes in many strange forms, many of which are still unknown," Paulsen said.