A FACELESS and brainless fish, flame shell beds and giant mussels were just a few of the discoveries made in 15 marine surveys during the year.

The surveys by Marine Scotland covered more than 2000 square miles and furthered our knowledge of the biodiversity of Scotland's seas.

Off the west coast, very rare fan mussels were found – at up to 18 inches long, Scotland's largest sea shell. Around the Small Isles, more than 100 specimens were discovered, the largest aggregation in UK waters. With golden threads so fine they can attach to a single grain of sand, seamen once believed they fed on drowned sailors.

The prehistoric "faceless and brainless fish" Amphioxus was found in the waters off Tankerness in Orkney. This elusive, rarely seen species is regarded as a modern representative of the first animals that evolved a backbone. With a nerve cord down its back, this strange fish has no specific brain or face.

The largest horse mussel bed in Scotland was revealed in waters near Noss Head, Caithness. Horse mussels stabilise mobile seabeds and provide a critical ecosystem for other species. Known as Clabbydhhu in Gaelic (translates as "enormous black mouth") these slow-growing molluscs can live to nearly 50 years old.

Other finds included flame shell beds in Loch Linnhe, Argyll, a cryptic species with bright orange feeding tentacles only found in very few west coast locations.

Meanwhile, new communities of northern feather star – a brightly coloured species with 10 feather-like arms fanning out from a central disc – were revealed off the Sound of Canna. Environment Secretary Richard Lochhead said: "In an age where the lands of the world have been mapped out and recorded, it's amazing how many discoveries are waiting to be found under the waves.

"The waters around Scotland are rich in such fascinating biodiversity and it's our responsibility to protect this fragile environment. That's why we have ramped up our marine survey work, with plans being prepared for new surveys in 2012 to further our knowledge of what lies beneath Scotland's seas."

The survey benefited from the use of the latest technology, with acoustic multi-beam scanners used to create 3D images of the seabed. As a result, first-ever marine maps of many new areas were possible, including waters around Rockall, to the west of the Outer Hebrides, around the Isle of Canna and within Sinclair Bay in Caithness.

Susan Davies, director of policy and advice with Scottish Natural Heritage, added: "Working with scientists from our partner organisations has not only been enjoyable, pooling our resources has enabled us to cover a far greater area and learn so much more about the life our seas support.

"The findings from these surveys will help us to manage them sustainably and ensure future generations can also enjoy the benefits of a healthy and diverse marine environment."

Dan Barlow, of WWF Scotland, said: "From helping inform the appropriate deployment of marine renewables to supporting the roll-out of a network of Marine Protected Areas, these survey findings will prove invaluable in helping ensure the recovery of Scotland's seas."