gramandy's picture

Flat Periwinkle

Observed: 27th March 2013 By: gramandy
Kent Wildlife TrustThanet Coast ProjectWildwood Trust
gramandy’s reputation in Invertebratesgramandy’s reputation in Invertebratesgramandy’s reputation in Invertebratesgramandy’s reputation in Invertebrates
Flat Periwinkle
IMG_1656a
IMG_1659a
Description:

Annual emptying of Thanet's largest tidal pool (at low tide end would be 5m) Found in eulittoral, submerged probably some of the time here, when the sluice gates are shut. Such a flat spire thought this had to be different.

Identifications
Species interactions

No interactions present.

Comments

nightfly's picture

Hi Graham, I agree the spire

Hi Graham,

I agree the spire isnt right for Ll. Edible periwinkle has a pointed spire as the other examples in the carousel show. This is more like the shape of the Flat Periwinkle with the flat pointless spire, but having looked at Flat Periwinkles recently there seems to be more than one species and the size of the opening seems to seperate them.

Have a look at this paper on Littorina obtusata and Littorina mariae-

http://www.invertebrate-challenge.org.uk/fieldstudies/documents/vol7.3_2...

Its not the one I wanted to share which I read a few months back, when I find it I'll share it. It went into opening detail and from memory, it said one species had a very large opening, the other very small but certain individuals couldnt be seperated on this feature alone as there is an overlap.

The flat periwinkles seem to be a bit tricky.

Cathal.

gramandy's picture

colour..

...location and loads of other ID notes don't hit home with flat peri as I thought this might be. Don't like the spire but opening just like Ll. Definitely not a topshell either.

nightfly's picture

It looks right for a flat

It looks right for a flat periwinkle, its quite distinctive and not easily confused with edible/common periwinkle or a topshell.

What other ID notes dont hit home? It looks ok to me, if its found in Britain then location is fine.

Cathal.

nightfly's picture

http://species-identification

http://species-identification.org/species.php?species_group=mollusca&id=774

On this page it mentions 3 colour morphs of Littorina obtusata- reticulata being green, brown or black. Maybe that ?

Cathal.

nightfly's picture

Sorry Graham, this is the

Sorry Graham, this is the last link- good diagram here of the differences in opening of Littorina obtusata and Littorina mariae. Yours seems to match obtusata better than mariae?

So we could be looking at the colour morph reticulata as mentioned above, I wonder would that be Littorina obtusata reticulata, or just Littorina reticulata?

http://www.seawater.no/fauna/mollusca/obtusata.html

Cathal.

nightfly's picture

Hi Graham, I dont think

Hi Graham,

I dont think there's anything else it can be to be honest, opening and colour are fine, its a very variable critter colourwise.

Cathal.

dejayM's picture

searching

I have searched iSpot for references to mariae/fabilis/obtusata
In this case the shell thickness and flatness allows me to agree with Graham.
It must be nigh-on impossible to separate the various morphs of L. obtusta from colour alone because of regional differences, food plant and, possibly, pollution. But the scientific separations DO seem to be based on pattern and colour.
As for L.mariae, Cathal, that is now called Littorina fabilis - though I s'pect you knew this.
If you want a real challenge, see here -
http://www.ispot.org.uk/node/328860
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