To make things worse, Mytilus galloprovincialis is widely invasive and
has similar issues of morphological similarity and hybridizing as
edulis and trossulus. Because trossulus was native to the west coast
of North America, the invasion by galloprovincialis went unnoticed for
decades.
On Sat, Jun 2, 2012 at 2:22 PM, Paul Mikkelsen <[log in to unmask]> wrote:
> John... et al.
> This Mytilus "edulis" vs "trossulus" distinction is consuming yet another of
> my weekends...  and I thank you VERY much for your help and thoughts on
> this issue of visual differentiation of them.  Any additional input, from
> anyone, is surely welcome! The need for DNA analysis to differentiate
> species is troublesome to those without such expertise, equipment, time and
> facilities to conduct such work.
>
> I have found one report which compared multiple physical shell
> characteristics M. edulis (N=117) and M. trossulus (N=100), and which found
> significant differences. One of their general concluding statements was
> "Shell shape for M. edulis was more eccentric compared to M. trossulus which
> was more elongated."Â Â [I'm reading/absorbing this report in its entirety
> later today]
>    Innes, D.J. and J.A. Bates. 1999. Morphological variation of Mytilus
> edulis and Mytilus trossulus in eastern Newfoundland. Marine Biology
> 133:691-699.
> Â Â Â http://www.mun.ca/biology/dinnes/Innes.pdf
>
> The following page (Paul van Poppelen)Â has side-by-side images of M. edulis
> and M. trossulus. MY thoughts on the (adult?) images are that the "top
> margin" of the shells of M. edulis are more angulate, and both margins of
> the shells of M. trossulus are somewhat curved. The height:length ratios
> seem different, with Mytilus edulis being higher for its length.
> Â Â Â http://faculty.chml.ubc.ca/sbaldwin/poppelen.html
>
> However, this is inconsistent with other images (plates 1 and 2, on the 1st
> link below) and various reports state that this shell variability (see other
> links) may be influenced by environmental conditions, and population
> density, as well as hybridization..    Ugggh!!!!
>
> http://naturalhistory.museumwales.ac.uk/britishbivalves/browserecord.php?-recid=410
>
> http://naturalhistory.museumwales.ac.uk/britishbivalves/browserecord.php?-recid=107
> See also the bio for Paul Rawson:
>
> http://www.bily.com/pnwsc/web-content/Family%20Pages/Bivalves%20-%20Mytilidae.html
>
> Thanks John, for the clarification of the existence of M. trossulus in the
> N. Atlantic.
>
> I now even question the my ID of the multitude of shells of "Mytilus
> edulis"(?) that I recently collected in Falmouth, Maine.
> Â Â Â https://picasaweb.google.com/108580848782880140183/EAIMytilidae#
> Still looking for an EASY way to distinguish Mytilus edulis and Mytilus
> trossulus.
>
> As always:Â THANKS!
> Paul Mikkelsen
>
> PS:Â Thank you, John, for providing me with your May 18th post/thoughts...
> I did not receive them initially.
> Similarly, I periodically get CONCH-L posts that are replies to original
> posts that I didn't receive. Hmmmm....
>
> --------------------------
> On 6/2/2012 12:28 PM, John Maunder wrote:
>
> Hi Paul
>
> Don't know why, but some of my recent posts don't seem to be getting
> through.
>
> On May 18, I sent you the following reply:
>
> .....
>
> Hi Paul
>
> I have examined my museum specimens and have to AGREE with you that your
> unidentified mytilid specimens are NOT Modiolus, although they do LOOK like
> that taxon, at least superficially. The pitted resilial ridge business is,
> indeed, convincing. Also, the darkness of the inside of the shell in your
> photos, amongst other things. And I think I can see dysodont teeth in one
> photo ["Unidentified specimen #2 --- hinge"]?
>
> However, I am still not convinced that you have true M. edulis. Something,
> even beyond the off-centre umbo, is just not right about the specimens.
> Nonetheless, you may well be looking at something in the "M. edulis
> complex". Have you considered M. trossulus? This Pacific species is
> naturally occurring on the east coast of N. Am. [and in Europe], especially
> in the Canadian Atlantic Provinces. While a little darker in colour, it is
> very hard to distinguish from edulis without DNA analysis. And, BTW, the two
> hybridize. Any thoughts on how to reliably distinguish trossulus from edulis
> would be most welcomed.
>
> JOHN
>
> .....
>
> PS.
>
> It is interesting that you mention Mytilus trossulus in your recent post!
>
> I should point out that M. trossulus is NOT a recent "INVASIVE". It seems to
> have invaded the North Atlantic, via the Arctic, probably before the
> Pleistocene glaciation. It is long-established both in eastern North America
> and Europe.
>
> I have been looking at the region of the dysodont teeth, and am wondering if
> there might be a diagnostic feature here: the distance of the teeth from the
> apex, the wider extent of the "shelf" upon which the teeth reside, and the
> greater angle that the teeth are mounted on that shelf. Also the generally
> blade-like versus knobby nature of the teeth. The inside of the shell of M.
> trossulus tends to be darker, and the shell has a bit of a "hook" towards
> the apex. M. trossulus also tends to be found in more sheltered localities.
>
> The only way to be absolutely sure of what this means is to examine
> specimens that have been analysed for DNA. This is especially true since
> M. edulis and M. trossulus hybridize somewhat. Luckily, there is such a
> collection available to me (in the hands of David Innes, Memorial University
> of Newfoundland). I will try to examine it soon.
>
> I hope this post reaches you!
>
> JOHN
>
> ----- Original Message -----
>
> From: Paul Mikkelsen
> To: [log in to unmask]
> Sent: Friday, June 01, 2012 11:52 PM
> Subject: Re: [CONCH-L] ID help needed: Mytilidae (NW Atlantic) Modiolus vs
> Mytilus
>
> John,
> Any chance you've had a chance to examine the specimens that you referenced
> below?
> Presently, I'm trying to justify my ID of Mytilus edulis vs the North
> Atlantic invasive (from the west coast), Mytilus trossulus.
>
> I think that I may have a couple specimens of M. trossulus coming to me, for
> comparisons, but no guarantees.
>
> Thanks for any thoughts/insight that you may find time to provide.
> Paul
>
>
> Paul Mikkelsen
> 3705 Eleven Mile Road
> Fort Pierce, FL� 34945
>
> tel: 772-464-2085
> cell: 772-332-0712
>
>
> --------------------------
> On 5/15/2012 4:03 PM, John Maunder wrote:
>
> 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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--
Dr. David Campbell
Collections Assistant
The Paleontological Research Institution
1259 Trumansburg Road
Ithaca NY 14850
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