More than 100 million brightly coloured and rare shellfish have been found in Loch Alsh, a sea inlet between Skye and the mainland.
However, Flame Shell beds are vulnerable to mechanical disturbance, particularly from fishing boats using bottom trawls and dredges, and extensive beds are now rare.
The find is now to be afforded extra protection despite local fishermen saying there is no risk.
A survey commissioned by Marine Scotland, as part of its work to identify new Marine Protected Areas (MPAs), has revealed 185 acres covered by the small, scallop-like species.
It has several neon orange tentacles that emerge between the creatures' two shells. Flame shells group together on the sea bed and their nests create a living reef that support hundreds of species.
In one study in Loch Fyne, six nest complexes supported 19 species of algae and 265 species of invertebrates. Primarily associated with areas of accelerated tidal streams the best known examples occur in a number of sea lochs on the west coast – Lochs Fyne, Sunart, Carron, Creran, Alsh, Broom and lower Loch Linnhe.
Environment Secretary Richard Lochhead said the seas around Scotland covered an area five times bigger than the country's landmass, and supported many fascinating and beautiful species.
He said: "The flame shell must be considered among the most remarkable species in our waters, with a dazzling array of orange tentacles. Many would place such an exotic species in far-flung tropical reefs – not realising they dwell under the waves just off the coast of Skye.
"This important discovery may be the largest grouping of flame shells anywhere in the world."
The Loch Alsh survey was carried out by Heriot-Watt University on behalf of Marine Scotland.
Dr Dan Harries, of Heriot-Watt University's School of Life Sciences, said: "Too often, when we go out to check earlier records of a particular species or habitat we find them damaged, struggling or even gone.
"We are delighted that in this instance we found not just occasional patches but a huge and thriving flame shell community extending right the way along the entrance narrows of Loch Alsh. This is a wonderful discovery for all concerned."
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