dejayM's picture

Bean mussel

Observed: 28th May 2013 By: dejayM
Biological Recording In ScotlandHighland Biological Recording GroupOrkney Biodiversity Records Centre
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added 2014

One of two possibilities. I have 'gone' for Bearded (and not Bean) on the grounds of its description in my books, even though this is a very small specimen and is rarer in Orkney
Of course, it may still be Modiolula phaseolina - the Bean Horse Mussel
October 2014 - revisited, added TWO! IDs and another picture.
Changed the Title.
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Species interactions

No interactions present.


dejayM's picture

the Bean and the Bearded

When I encountered this it looked like some mystery ingredient in a cooking competition - I had NO idea what it was!
Like so many things underwater and under a rock, amid other small wonders, it almost defied description and was nearly discarded.
But a photo or two, at home, allows for a leisurely, though inconclusive, investigation.
Half an hour in my many books, 20 mins in the Internet cellar and, nearly and hour to form this post, well maybe - still only maybe!
It is not 'hairy' in the normal sense, it is small, the shell seems open and looks as though it would never close but that, I think, is an illusion.
I've never seen anything like it before and will probably never see another.
Distribution details are very vague but both the Bean (Modiolula phaseolina) and the Bearded Modiolus barbatus) are recorded in Orkney (via the NBN Portal) but far less so the Bearded Horse Mussel

ChrisMcA's picture

Am dubious on this. See

Am dubious on this. See as against
The barbatus is so-called as it has 'serrated spines' on it's periostracum ie outer skin

dejayM's picture


Like many of my slightly unusual 'finds', there is a dubiousness - based upon my lack of detailed observation.
I pondered long and hard, looking for the clues you mention. But there are pictures of both, in either coats and cross-descriptions, proving, as far as I can tell, that the Internet is NOT the best portal for an amateur. Ha!
But I spent quite a while in Hayward & Ryland, reading over the quite meagre descriptions.
This morning, in 'Collins' Pocket...' I found Limaria hians and nearly whooped until I read further and looked in Google Images. Ha!
Chris, your continued attention is appreciated; it seems to me that this sort of interaction is a major part of the purpose of iSpot.
I have added the alternative as an ID.

ChrisMcA's picture

Limaria hians, especially

Limaria hians, especially swimming, would be a dream come true. But I've only just noticed The Collins' bk illustrn shows the detail of barbed v smooth spines.

dejayM's picture

A dream then - maybe

First this The announcement was made in December, my pictures are dated June.
Whilst mine does not show the glory of the animal, nor the expected paleness of the shell, the pictures show a decent resemblance. We have to bear in mind mine was found in shallow water and, indeed, it may been beached, even dead.
I now doubt the other two possibilities (the IDs) because I am now far more experienced at reading keys and clues; notwithstanding ChrisMcA's doubts (and dreams!)
I have posted the pictures to the Marine Conservation Society in the hope they might offer a definitive ID.
It still might be M.phaseolina - "small, oval 20mm long...short smooth periostracal spines."

ChrisMcA's picture

L.hians hasn't any spines on

L.hians hasn't any spines on it's shell

dejayM's picture

Fourth ID

Thanks. You're right of course Chris. But I thought it worth a record (as a proposed ID) because each will get discarded and each will have its merits discussed again (I hope). I entirely agree that Limaria hians is really out of the question (now), largely because of what you say and the shell structure which, if L.hians, would be much lighter and somewhat crenilated at one end.
My feeling here, now I am a TINY bit more experienced, is that it might be an immature Modiolus modiolus (true Horse Mussel) -
"Young shells have numerous long, smooth, spines which wear away in the adult. The interior of the shell is white. The shells reach 10cm long by 12-18 years, but can be up to 22cm." where there is more useful description
There is an impressively similar shell here - (USA)
And this, more or less, confirms it
There is no mention of spines nor hairs in the COLLINS Pocket Guide and, to be frank, the small alternate diagrams of spines is not well attributed to any of the three modiolula.
You have agreed with Modiolula phaseolina and I don't blame you; but I have now put up Modiolus modiolus for your (and others hopefully) consideration.

dejayM's picture

Run its course.

"I reckon this is probably Modiolus modiolus. The projections on L. hians are part of the mantle (soft tissue) rather than part of the shell, as in this case. I've attached the ID sheets from the Museum of Wales website, which are probably the most useful literature." Centre for Marine Biodiversity and Biotechnology - Heriot-Watt University.
Those sheets are not conclusive but are strongly indicative of this being M.phaseolina (MY opinion) - mostly because of the bluntly rounded umbone (seen in Picture 4); and also because the shell appears clearly to be covered with spines - many illustrations show M.modiolus with no such obvious embellishment.
But my pictures show a very small example, so it is immature.
I think this has run full course, perhaps until I get another and boil it down to an empty shell and thus separate it from the other, which might (only might!) show small crenulations on the outside and minor hinge differences.
>>Modiolula phaseolina<<
>>Modiolus modiolus<<