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You may be safer in restricting yourself to the Genus, though i agree this is probably Patella vulgata apparently it is impossible to tell this difference between this and other UK Patella sp. without a view of the underside.
This is P.vulgata....honest. As a rocky shore ecologist I've ofen been faced with making field counts. With a lot of practice the separation is possible without turning them over, otherwise I'd be responsible for countless deaths. Forcing a limpet off the rock generally ruptures the foot muscle and looses an often fatal amount of body fluid.
Separating P.vulgata and P.ulissiponensis can be hard when dealing with eroded anomals or working with animals in the low shore covered by weed.Generally P.u appears to have more radiating ribs without any one of the being strongly developed. The identification of P. depressa is easy enough as the shell apex is anterior of the mid line and there are a pair of strongly developed shell ridges in the posterior part of the shell. Juveniles are very easy as both P.d and P.u have characteristic black and white patterns.
The barnacles are Chthamalus montagui and the topshell is Osilinus lineatus.
Thanks for that Mike, i only commented as a previous ID of mine as 'overturned' and that was the reason they gave. However, to be honest at the time i didn't know better anyway. Now thanks to you i do!
A lot of practice is vital to separate limpet species without damaging them but a bit of ecological knowledge helps too.
P.ulyssiponensis are seldom seen in the upper half of the shore and even in the low shore they tend to favour pools, pool edges or permanently wet places; they are seldom out on open rock among the P.vulgata.
As I mentioned elsewhere, the shape of P. vulgata changes as one moves downshore. At the top they tend to be large and tall while lower down they are far faster growing, shorter-lived and flatter; big limpets low down on the shore are often P.u.
In the picture we have tall limpets among the high shore barnacle Chthamalus montagui. In Cornwall tht leaves P.d or P.v as the choices for an ID.
P.depressa tends to be on the upper half of the shore too but has a tendency (no more then that) to be out of shade on the sunny side of rocks or reefs.
P.v is found all around UK. P.u doesn't live in the southern North Sea; P.d is a south west species getting as far north as Anglesey and is not found in Ireland (despite a few dubius records).
Thanks very much, this field knowledge is very useful.
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