dejayM's picture

Flat Periwinkle variation

Observed: 29th April 2013 By: dejayM
Biological Recording In ScotlandHighland Biological Recording GroupOrkney Biodiversity Records Centre
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Allsorts; live and bright ones are hard to find; empty shells easy.
The pair-pictures are live from the very same pool. Might this be camouflage adaptation or response to coloured food?

Species interactions

No interactions present.


gramandy's picture

Hi Derek...

...not very mammally?

trudy-russell's picture

I have agreed but its worth

I have agreed but its worth noting that Littorina fabalis is almost identical (penis tip length is the distinguishing feature!) so you cannot be certain of the ID. L. fabalis occurs lower on the shore and is more tolerant of exposed shores but they do overlap! L. fabalis is usually found on Fucus serratus and L. obtusata prefers Ascophyllum nodosum but again there is some overlap! Obviously with your shells none of this helps

Trudy Russell
Marine Advisor
Natural England

To find out about what's going on in the south west check out

dejayM's picture


Oh welcome Trudy. How nice to get new and powerful interaction.

Is Littorina fabalis L.mariae? I ask because NBN seems to hate fabalis Marlin too!
Whichever it is I bet we have millions, mixed with obtusata - they are both recorded here.

And I now see, the left of my foursome might be Littorina obtusata var. reticulate.

gramandy's picture


...and L.mariae - one and the same at the moment - watch this space.

dejayM's picture


You're right Graham - much more molluscan. Thanks

gramandy's picture


...size generally smaller (but not always) and lower down the eulittoral zone (but not always) - the ratio of the opening to shell width can also help (fabalis being a smaller opening). Agree about genitalia though being much more discerning (Trudy - you haven't mentioned the angle of the dangle though) - leave his privates alone it's one thing turning them over and disturbance this way but please.... (then again you need to distinguish the gender).

Flat, rough, you can never be sure of the ID these days (thank goodness, there is only 1 edible at the moment - although that is now debatable).

So, I too have agreed on the basis of shells found presumably higher up the eulittoral zone (as they are shells only?), but I think I may have mentioned a pic of the opening before, always helps!

I'm almost persuaded that pic 4 opening could be fabalis (ratio of length/size of opening and appearance of small opening). If you turned the shell over showing the opening, so that we could see the spire at the top, fabalis has no spire at all whereas obtusata is discernible.

dejayM's picture


Just going over old ground...tidying up...intensifying mystery
But I have moved on a bit - three weeks' more experienced!