THE Bearsden Shark, an affectionately named fossil discovered near Glasgow two decades ago, has finally been officially revealed as a new species of fish, and named akmonistion zangerli, more than 330 million years after it became extinct.

The akmonistion zangerli has been on display in the city's Hunterian Museum for almost 20 years, but was known simply as the Bearsden Shark because of where it was found.

It was excavated by Stan Wood, a Scottish fossil collector, in 1981 and has since been studied in microscopic detail and compared with other fossil shark remains from around the world.

Its new scientific name - akmonistion is from Greek meaning ''anvil sail'' and zangerli is from the name of a fossil specialist - was announced yesterday to show it is different from all other previously discovered animals, whether fossilised or living.

The discovery that it was a new species was made by Mike Coats, of Chicago University, and Sany Sequeira, of Birkbeck College, London, whose re-search is published in the Journal of Paleontology.

The fossil is the best preserved shark of its time. Although it was identified as being a variety of stethacanthus, scientists knew no more about its genus or species.

From the tip of its nose to the end of its tail, the shark's cartilage skeleton is still intact after spending 330 million years locked in a muddy swamp in Bearsden. Even the partially digested remains of its last meal are inside the one-metre long fossil.

Neil Clark, curator of palaeontology at the Hunterian Museum, said: ''Three hundred and thirty million years ago, there was a brackish water lagoon extending at least from Dalry to Milton of Campsie and south of East Kilbride. The fossils are so exceptionally well preserved that I have even found the remains of muscles and blood vessels preserved in some.

''The shark, along with other animals, must have become buried in thick soupy oxygen-deficient black mud rapidly, preventing scavengers from de- stroying these unique fossils. Although the fossil has been given a new name, I am sure it will continue to be affectionately called the Bearsden shark.''

It is on display at the museum, which is open from 9.30am to 5pm, Monday to Saturday.