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In my (very) limited experience common Limpet is more rough looking - I inclined to agree with liziwig.
BMIG website: www.bmig.org.uk (centipedes, millipedes & woodlice)
BMIG Newsletters ~ www.bmig.org.uk/view/resource/bmig-newsletter
BMIG Bulletins ~ www.bmig.org.uk/view/resource/bmig-bulletin
Ordinarily and not long ago I would have agreed to Common limpet. But they are really quite difficult to tell apart via just a top-view. Personally I would rather see these titled Limpet but with notes suggesting that they might be one of, perhaps, three.
I have been through this several times with an expert, including having empty shells to hand, to the conclusion that it really IS hard to tell them apart unless one can see the animal or at least the underside - which usually means killing it.
That it is common and that other examples can be seen as close lookalike, is no proper evidence. This is really VERY unfortunate.
I feel like a spoilsport because I have agreed to a few Commons in my quite short time here - though there probably is no harm in that..
I have read and read, talked to experts, posted a few and STILL believe it might be impossible to tell.
There are a good number of limpet Observations, http://www.ispotnature.org/node/646438 is one of mine. Despite me making it easy for people to agree, there are still none.
And here is my only slightly more educated post http://www.ispotnature.org/node/648659 in which I have written -
"It is very difficult to find definitive information which allows correct separation of the three most common ones and a huge overlap in descriptions of each. Book illustrations are somewhat vague and the internet is loaded with pictures which do nothing for separation."
Jan Light's "straightforward" Guide is here http://www.glaucus.org.uk/Limpets.htm She writes "With practice it is possible to discern these differences and make accurate judgements based on exterior appearance but it is not foolproof even for the ‘experts’" Oh dear then!
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