Images of the three-year-old freshwater pearl mussels Microscopic three-year-old freshwater pearl mussels
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* Action to safeguard rare mussels
* Freshwater pearl theft increasing
Scottish freshwater pearl mussels join giant pandas and Javan rhinos in a new book listing 365 of the world's "most endangered species".
Species on the Edge of Survival has been put together by the International Union for Conservation (IUCN).
It keeps a red list of threatened wildlife using information gathered by scientists and conservationists.
The IUCN said the list was the most complete scientific knowledge on the conservation status of known species.
The new book, published by Collins, includes the pearl mussels because of the threat posed by poachers and habitat loss.
In 2010, a survey suggested about 75% of the country's internationally-important pearl mussel sites had been damaged by criminals.
Criminal acts ranged from illegal pearl fishing to unauthorised river works which resulted in the destruction of entire pearl mussel populations.
Scottish Natural Heritage (SNH) said the destruction was "shocking".
The mussels are protected under the Wildlife and Countryside Act 1981.
Wildlife crime officers and SNH launched Operation Caesar to safeguard the future of the species in Scotland.
Scotland has a total of 21 designated sites for pearl mussels, with Scottish rivers holding about half of the world's population of the species.
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