Great Barrier Reef: Swimming in a cave of feeding sharks
30 December 2011 Last updated at 11:10 GMT
Most of us know that Australia's Great Barrier Reef is one of the natural wonders of the world, but did you know it is home to sharks that walk on land and deadly snails that hunt fish?
In a new BBC series presented by the marine biologist Monty Halls and produced by James Brickell, the team encountered some extraordinary sights in their year-long project.
Great Barrier Reef, BBC Two, 1 January, 8pm