I've just read an article in 'Mammal News' from the Mammal Society, which refers to the water vole as Arvicola amphibius. When did this change from A. terrestris? (Have to say, amphibius makes much more sense than terrestris!)
I've no idea, I've always refered to it as A terrestris. To confuse matters Wikipedia calls it "A. amphibius (formally A. terrestris)" !
The National Biodiversity Network(NBN), from whom iSpot gets its scientific names, uses A. terrestris.
The clincher for me is what does the 'bible' say? The current 4th edition of the Mammals of the British Isles (Harris and Yalden) uses A terrestris and so did the 2nd edition published in 1977. It also lists past alternative names; A. ater, Mus amphibius and Mus terrestris but NOT A. amphibius. Therefore, the implication is water voles have never officially been known as A. amphibious. However, I do agree the name fits it better than A. terrestris.
Other common names include obvious ones like water rat but also some wierd ones; craber, waterdog and earth hound.
I asked a friend of mine who studies aquatic mammals and he referred me to a discussion on the NBN website.
It appears the final, official discussion is (drum roll....)
The article on Wikipedia explains why. So NBN need to change their database and Harris and Yalden have an excuse to produce a 5th edition, thats another Â£75 I'll need to find!
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