The smallest, lightest animal with a backbone has been described for the first time, by scientists in the US.
The stout infantfish lives exclusively in Australia's Great Barrier Reef and the nearby Coral Sea
The minuscule fish, called a stout infantfish, is only about 7mm (just over a quarter of an inch) long.
It lives around Australia's Great Barrier Reef and has snatched the "world's smallest vertebrate" title from the 1cm-long dwarf goby fish.
The infantfish, which is no longer than the width of a pencil, is described in the Records of the Australian Museum.
The first specimen of the tiny creature (Schindleria brevipinguis) was collected way back in 1979, by the Australian Museum's Jeff Leis, during fieldwork in the Lizard Island region of the Great Barrier Reef.
But the fish was not properly studied for years, until HJ Walker of the Scripps Institution of Oceanography, California, US, and William Watson of the Southwest Fisheries Science Center, La Jolla, US, picked up the case.
"It was a really good day when I first looked under the microscope and recognised something that I knew was a new species," said Dr Walker. "But at the time I didn't realise that I was looking at the world's smallest vertebrate."
Only six specimens of the stout infantfish have ever been found.
The females - at around 8.4mm - seem to be bigger than males, who usually measure in at a diminutive 7mm. They are what scientist term "paedomorphic", which means they retain many infantile characteristics, even when adult.
The stout infantfish gets its name from its babyish features, and the fact that it is unusually stout compared to other species of infantfish.
Its tiny frame is matched by its short lifespan, which is thought to be a mere two months. This quick turnover might actually work in the fish's favour, allowing it to keep up with a world that is changing fast.
"It's interesting that these animals experience several generations a year," said Dr Watson. "This suggests they could evolve quickly as well.
Scientist HJ Walker with a jar holding the World's smallest vertebrate
"They live in a specialised habitat that could be threatened by global warming or human development, but they may have the ability to evolve as fast as their environment changes."
Philip Hastings, the curator of the Scripps Marine Vertebrates Collection, says the identification of the stout infantfish is another demonstration that scientists do not yet have a complete picture of marine animals.
"Anytime a scientist identifies an 'extreme' in the world it is important," said Dr Hastings. "Think about the whole envelope of life. Most of us systematists describe things that fill in the dots in the middle of the envelope.
"This new discovery is pushing the edge, increasing the size of the envelope.
"It's important because it demonstrates that we're still expanding our knowledge of the limits of the diversity that's present on this planet and there are still significant discoveries to me made."