The Cockles: Common vs Lagoon

[Max-fossils]

Hi all,

 

So the Cerastoderma genus has (in addition to a few other fossil species) two extant species: C. edule (common cockle0 and C. glaucum (lagoon cockle). 

Both of these species appear (both fossil and modern) here in the North Sea, and their Eemian fossils are common finds at the Zandmotor.

 

Now I have always been told, and read in most of my books, that the difference between them is that:

 -> if you draw a vertical line from the umbo downwards, C. edule is pretty much symmetrical while C. glaucum will have one side more stretched out. As can be seen in the picture above. Pretty straightforward.

 

Plus, this is what I explained in one of my old Instagram posts:

 

 

But, while searching a bit around, I just now saw on the Wikipedia website a picture of a symmetrical cockle that they claim is C. glaucum. And WoRMS also has some pictures of some more or less symmetrical cockles for the lagoon cockle! So I am very confused...

 

What is the difference then between the two species? 

 

Looking forward to your answers!

 

Best regards,

 

Max

[oldtimer]

My guess looking at them is the horizontal bands are different.  With very pronounced ones on Cerastoderma glaucum.

[Max-fossils]

On 2/18/2018 at 5:47 AM, oldtimer said:

My guess looking at them is the horizontal bands are different.  With very pronounced ones on Cerastoderma glaucum.

(Sorry for such a late reply... )

 

No, that's not it. The bands are just a reflection of what the color pattern was like when the shell was alive. I have examples of both species with either bands or none, so that can't be it. Thanks for the help though. 

[Darko]

But how to recognize if it`s fossilized or not? I do have like 50 of them from La Manche Channel.  Cerastoderma glaucum mostly, i compare them with one which i`ve got from Max two years ago and they are very similar. I don`t know what to say. If someone know anything about La Manche marine fossils let me know.