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Mytilus trossulus?
01-10-2013, 05:51 AM,
Mytilus trossulus?
Hello everybody!

In December I was in Copenhagen, Denmark, and on Amager Strand beach, 5 mins from Copenhagen city centre I found the following Mytilus specimens. I have done some research on the internet (I am not a Mytilus expert) and have found out that in the Copenhagen area Mytilus trossulus or a hybrid between Mytilus trossulus and Mytilus edulis is prevalent. I have taken pictures of all the Mytilus specimens I collected and I really need your help to decide whether they are Mytilus trossulus, Mytilus edulis or what the internet calls Mytilus edulis f. trossulus. I think that some of them are clearly (and based on the images I have found on pages like <!-- m --><a class="postlink" href=""> ... -recid=410</a><!-- m -->) are Mytilus trossulus.

Please, can anybody help?

Many thanks!


1. Trossulus
[Image: P1090272.JPG]

2. not sure
[Image: P1090271.JPG]

3. single valves, top view
[Image: P1090273.JPG]

4. single valves, first close-up
[Image: P1090274.JPG]

5. single valves, second close-up
[Image: P1090275.JPG]

6. single valves, third close-up
[Image: P1090276.JPG]

7. single valves, fourth close-up
[Image: P1090277.JPG]

8. single vales, inside view
[Image: P1090278.JPG]

[Image: P1090279.JPG]

9. Hinges
[Image: P1090282.JPG]

[Image: P1090280.JPG]

[Image: P1090283.JPG]

[Image: P1090285.JPG]

10. Other specimens:

[Image: P1090286.JPG]

[Image: P1090287.JPG]

[Image: P1090288.JPG]

[Image: P1090289.JPG]

[Image: P1090290.JPG]

[Image: P1090291.JPG]

[Image: P1090292.JPG]

[Image: P1090293.JPG]

[Image: P1090294.JPG]

[Image: P1090295.JPG]

[Image: P1090296.JPG]

01-10-2013, 09:34 AM,
Re: Mytilus trossulus?
I am no Mytilus expert either, but looking at the photos I would say (judging by the position of the beaks and the straightness or otherwise of the ventral margin) that you have a mixture of both species plus maybe some hybrids.
I know in Loch Awe (?) trossulus lives but only at the rear of the Loch, in the area of lower salinity. Further down and at the mouth edulis takes over but they do hybridise there at the transition zone.
I think they can only be reliably told apart by the soft parts rather like galloprovincialis.
01-10-2013, 09:35 AM,
Re: Mytilus trossulus?
P.S. I visited Copenhagen a couple of years back but never got near the sea. I did however collect on various other parts of North Sealand and found a few things, the best was a few pieces of Baltic amber.
01-10-2013, 11:53 PM,
Re: Mytilus trossulus?
Thanks Dave!  Wink I had a feeling it wasn't going to be as easy as I had hoped.
Well, we went to Copenhagen to visit my sister-in-law who was doing Ph. D. studies in chemistry until Christmas. Before we went I researched the beaches on the internet and found two:

Amager Strand about 5 minutes from the centre on the S-train, and another one in the opposite direction which as 10 mins. away.

We went to Amager Strand, but it was covered in snow. Only the strip by the shore was snow-free.
On seaweed we found tiny, curious ram's horn-like shells and I though they might be Spirula spirula, but I'm not sure.

01-12-2013, 12:56 PM,
Re: Mytilus trossulus?
I stayed in Denmark for a month a while back, I lived in Hillerod but went to a few beaches on the North of Sjaelland around the Hundested area (worth a visit if you go there again!). Not much in the way of shells really, not helped by there being hardly any tide! I did find some interesting Littorinas on the rocks and a few bivalves on the beach. The best place was in the Harbour where the fishing boats wash their nets out, found a pile of Modiolus modiolus mixed in with Cyprina arctica and a few other odds including my first Capulus ungaricus.
Denmark is a beautiful country, I fell in love with it on my first visit for a week in the Summer of 2011. That is when I visited Copenhagen with the friend I was staying with. A beautiful city with spectacular Botanical Gardens and a really nice geological museum. One day I hope to go back there but it does have a few bad memories. Long story!
01-13-2013, 02:30 AM,
Re: Mytilus trossulus?
Francesc and I were only in Copenhagen for 3 days, and while Francesc's sister was at the university we did our own thing. We visited the Natural History Museum (I wanted to see how their shell collection faired against mine Wink ). We also went to the Amber Museum, the Guiness World Records Museum and the Ice Bar. We didn't really have much time. We had wanted to go to the Viking Museum, but it was too far away.

I think that you were really lucky to find Cyprina arctica and Modiolus modiolus; I found lots of Mya arenaria and also Cerastoderma. However, the Cerastoderma I found are pretty coloured, and I was wondering if there was a possibility they could be Cerastoderma glaucum. I know I have asked this before with some Cerastoderma I found at the Ebro Delta, but any pointers on how I can distinguish the two Cerastoderma?

To be honest, the best thing for me was the Christmas spirit. Sadly I lost my mother two years ago at Christmas to cancer, and seeing all the Christmas trees and the decorations and light brought back a bit of the essence of celebration I had lost. So, for me and in this sense, it was great!

Thanks for replying! Smile

Best wishes,

01-15-2013, 11:37 AM,
Re: Mytilus trossulus?
I never got to those but intend to one day. I did visit the Viking Ships Museum when I went in the Summer, which was fantastic, and a Viking village, which was closed! 

Regarding C. glaucum, the best way of telling is the salinity of the habitat, they like lower salinity than edulis.  Also they are a lighter shell in weight and there are structural differences which can be found online.
I have found prettily coloured edulis here in England, but they tend to be young ones.

I never got to Copenhagen during Christmas but celebrated with a traditional Danish Christmas dinner in Hundested with a large group of people, it was really great. New year was unbelievable, they sure like their fireworks there. Many more than here on November the 5th!

Sorry to hear of your loss, I lost my Mother around 4 years ago now. Always a blow to lose someone close.

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