nightfly's picture


Observed: 22nd February 2013 By: nightflynightfly’s reputation in Invertebratesnightfly’s reputation in Invertebratesnightfly’s reputation in Invertebratesnightfly’s reputation in Invertebratesnightfly’s reputation in Invertebrates

Can someone help with an ID for these please? I thought these were Chinaman's Hats (Calyptraea chinensis) but they are too big according to the info in the MarLIN website. It gives a size of up up 1.5cm across and .5cm high. Biggest one here is 2.3cm across and 1.5cm high. Thanks.

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nightfly's picture

Hi Scubamann, I'd be

Hi Scubamann,

I'd be surprised if these were common limpet, but in the absence of an obvious identifcation?

Are you saying they are eroded to look as they do because they do not look like typical common limpets?


scubamann's picture


Hi Cathal,
The basic shape, size and colouration seems about right, the inside wall has no shelf (so not a slipper limpet) and yes once they have died and fallen to the sea bed they will wear smooth with the action of currents.
But I am not certain.

I am not familiar with your "Chinaman's hats" (maybe a local thing); only China limpet, Patella aspera, which is more straight sided and flatter.

Pedantically, whatever species they come from they are no longer and "organism" as it is only the shell - but we'll let that go!


nightfly's picture

Hi Geoffrey,Shells,

Hi Geoffrey,

Shells, feathers, bones and the like, basically any part of any organism can only be IDed on iSpot as belonging to that species. It is very common to do so on iSpot. Parts of a species cant be attributed to any species other than its own. Even droppings and footprints from animals are shared and IDed on iSpot as belonging to a species, it isnt a suggestion that the dropping or shell for that matter is the organism.

These little limpets are peculiar, they dont grow much bigger than the largest here- 2.3cm across. If it were just an eroded common limpet I would expect to find larger examples as well as these small ones. The shores I look for stuff on are littered with common limpet shells but these are quite different.

The chinaman's hat I mentioned is similar but according to MarLIN these are too big to be that:-


dejayM's picture


Origin 20 August 2015
Ordinarily and not long ago I might have agreed to Common limpet. But they are really quite difficult to tell apart via just a top-view (which this is certainly not). Personally I would rather see these titled Limpet, from the beginning but with notes suggesting that they might be one of, perhaps, several.
I have been through this many 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, 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 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 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!
PS Edited for spelling corrections

nightfly's picture

Hi Derek,The ID of these

Hi Derek,
The ID of these shells troubled me for a few years. I found them on a very regular basis, they are easy to find. Since I made this post I have discovered what they are. This might raise a few eyebrows but I am pretty sure these are mature blue-rayed limpets.

I have heard that when they get this old they are inclined to live in the holdfast of the kelp rather than up the stipe.

At this age (2cm across+) the blue rays are rarely if ever visible, I had one nice example in the winter past, 2cm diameter and blue rays still visible.

For whatever reason, when they get really mature, they look nothing like the young shiny examples with the vivid blue stripes. They become comparatively ugly.

MarLIN saysd they go up to 2cms but I have got them to at least 2.5cm and possibly even a bit more.


dejayM's picture

Patella pellucida laevis

Yes, there's been a debate for years, if I am reading right. MsiP, ordinarily a good site, has Ansates pellucida (a synonym) as two species one - A. pellucida laevis as" dull and devoid of blue rays, though it may have red rays."
It was also known as Patina Pellucida which finds this (summary) where the second variety is specifically mentioned. And that (Patina pellucida laevis) leads to this (what we are looking for!).

Up until yesterday, I thought it was firmly established that there is only one species but that it migrates to the stalks and takes up residence for its later life.
However, Dave Fenwick (who we should all listen to), has this and this paper suggests I may need to think again
Marlin has this - read Additional Information
I dare you to add an ID as Patella pellucida var. laevis!
It is a great pity all this information, together with the various posts of Patella pellucida cannot easily be brought together - a project perhaps.

dejayM's picture

waking up

Well! probably. Certainly this one is acceptable and my agreement stands.
But one of these (the left of the three) has a 'limpet-like' radial structure. My experience with H.pellucidum is limited to small, maybe immature, ones (that I have posted). I remember that they are elongated, not round and narrower at one end - see My gut feeling was that they wouldn't change their overall shape as they mature.
I have shells like the ones in this post in my collection, deep, round and very lustrous inside (from erosion). Generally, they are bigger, but none show the blue rays as seen in the centre of the three in Picture 2 - because they are all Patella. From that one glimpse alone, I'd agree (and maybe will yet). I'll be back the morn, as they say!
And so I am really glad I woke you up and that you have moved on in knowledge. Excellent stuff..
There are NO mature shells to be seen in Google Images, nor much information regarding mature ones anywhere I can find - history in the making then!
They are Marine Invertebrates so should have the Habitat as Marine, perhaps Coastal is near enough but add the tag Marine anyway!
Whatever the outcome here it should carry the tag ProjectM1. Please?

dejayM's picture


Origin 20th
here's some amazing stuff
PS. Check THE tag, you forgot a comma after rural..

nightfly's picture

Hi Derek, Just a short

Hi Derek,

Just a short comment. I know there are no mature pics to be found online, thats pretty much why the ID of these shells remained a mystery for so long. It wasnt until I found them with the blue streaks intact that their ID became clear. Like in this one which I think you have already linked- which is round, conical and has blue dashes. The juvenile shape and characteristics seem to be of little relevance to the really mature shell-

Edit- just revising- the peak of the shell is still closer to one end of the shell than the other in the vast majority of these mature blue rayed limpets but its not nearly so much as in the young shells. They do take on a more conical profile but the cone can be far from smooth 'sloped', theyre often quite distorted in shape.

The one on the left above is possibly a different species.

Talk soon, thanks,