Hi Paul
Hmm. Not sure that I'm convinced ... resilial pits or not!
I will try to look closely at ~9.6 mm museum examples [plus smaller and
larger examples] of both Mytilus edulis and Moliolus modiolus from
Newfoundland later this week, and report back.
JOHN
----- Original Message -----
From: Paul Mikkelsen
To: Conchologists List
Sent: Tuesday, May 15, 2012 12:12 AM
Subject: Re: [CONCH-L] ID help needed: Mytilidae (NW Atlantic)
John, et al.
I have returned from Maine, where I "hit the jackpot" for specimens of (what
I strongly believe to be) Mytilus edulis. I may have collected several
thousand of them! The dead and clean shells had accumulated, thanks to many
tidal exchanges, in a wide and long crack in a concrete boat ramp (Town
Landing, Falmouth, Maine; 43.732314 N Lat., 70.204509 W Long.). See the
last couple photos added to:
https://picasaweb.google.com/108580848782880140183/EAIMytilidae#
These specimens (a few mm to over 30 mm in length) are identical, in every
way, to the "mystery specimens" that I mentioned when I started this thread
on CONCH-L. These fresh specimens, in great abundance, approach the size
ranges that I might expect to coincide with the mystery specimens, had some
been allowed to grow.
John: first, thanks for your input and persevering with getting it thru.
I agree and disagree with you. I too see the off-center umbo, and this has
been pointed out previously (David Campbell, 4/25/2012 post to the list).
However, the "mystery specimens" as well as many specimens of the present
lot that I've examined all have resilial pits! According to Harry Lee
(4/25/2012 post) these resilial pits will only occur in three genera:
Mytella, Mytilus, and Perna. This eliminates Modiolus from consideration.
These pits are VERY evident in all of my juvenile specimens, as well as a
few quite mature specimens of Mytilus edulis that I also collected recently
in Maine. Also, looking at beached valves and freshly collected live adult
shells of Mytilus edulis (of unquestionable ID!), I can't say that the umbo
of the juvenile portion of the adult shell isn't offset a bit.
To examine/compare resilial pits in another genus, my local grocery store
yielded (for a price!) a box of farm-raised Green Mussels, Perna
canaliculus, from New Zealand. I "sacrificed" a few of these for
microscopic examination... voila! resilial pits!!! ...just like in all of
my Mytilus specimens.
In Maine, my beachcombing yielded one valve of the Northern Horse Mussel,
Modiolus modiolus. The umbo is definitively offset... no question. The
interior of this one large, mature (92 mm) valve was highly calcified,
obscuring distinct definition of pallial lines... [this also noted in the
abstract by:
N.A. Anwar, C.A. Richardson and R. Seed; 1990. Journal of the Marine
Biological Association of the United Kingdom; 70:441-457.
http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=4368464
That said, the Modiolus specimen seemingly had a much more robust pallial
sinus than my adult Mytilus edulis.
Additionally, the resilial pits are totally lacking in my specimen of
Modiolus.
All that said, I'm sticking with the ID of Mytilus edulis, despite the
offset umbo of these juveniles...
These images (labelled Mytilus edulis) also show off-center umbos:
http://www.marbef.org/projects/settlement/photo_gallery.php?album=642&pic=12451
http://www.marbef.org/projects/settlement/photo_gallery.php?album=642&pic=12452
http://www.marbef.org/projects/settlement/photo_gallery.php?album=642&pic=12453
and plate #2, showing VERY young specimens, on this page:
http://naturalhistory.museumwales.ac.uk/britishbivalves/browserecord.php?-recid=107
If anyone would like to pursue this further, and/or would like to have a set
of variously sized specimens from my recent collection effort in Maine, I
can surely spare a few specimens! If so, please contact me offlist with
your mailing address.
Again, THANKS to all!
Paul Mikkelsen
------------------------
On 5/13/2012 2:06 PM, John Maunder wrote:
Hi Paul
I sent the following reply to the Group just before leaving for 2 weeks in
Cuba [we Canadians go there a lot!]. Upon my return last night, I noted that
the reply did not make it onto the CONCH-L Listserv. Don't know why.
If this try does not work, maybe you could forward it for me. Thanks.
........
MESSAGE:
The off-center umbo would VERY strongly suggest a rather small Horse Mussel
... Modiolus modiolus (Linnaeus, 1758). This species is very common in
Newfoundland, so I have seen a lot of them, of all age groups. The shell is
definitely NOT M. edulis.
.........
John E. Maunder
Curator Emeritus of Natural History
The Rooms Provincial Museum
(... formerly known as the Provincial Museum of Newfoundland and Labrador)
St. John's, Newfoundland and Labrador, Canada
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