Thank you very much Dr.Mark for your kind input.

I do think these are oysters, Ostreidae. I see they have a single muscle scar that is somewhat central and appears to be tinted purple. That would suggest the genus Crassostrea. Do you have any other photos?

they do very much look like oysters

Thanks you very much Dr.Lofti , Dr.Susan and Dr.Steffen for your comments.

Kindly find yet another picture I took.

Yes, they look like a sort of cup-oyster. Is this a natural bed of this species?

Yes Dr.Alexandra.

Hi all,

the jagged shell outline I glimpse would suggest some species within Ostreidae

SALUTI

They look like Crassostrea, which location the picture was taken?

 Hi! Jackson.

This is Saccostrea cuccullata.

Best Regards,

M. Nithyanandan

I second Dr. Nithyanandan's identification. It is indeed Saccostrea cucullata (Born, 1778). Take close up images of the ventral margins where you can see V shaped arrangement

regards

Deepak

Jackson:

Yes, in a broad sense it can be considered as showing affinity to Saccostrea cucullata (von Born, 1778).

Best

Syed 

 Thank you very much Dr. Nithyanandan, Dr. Deapak and Dr. Syed for adding your answers.

Best regards

Jackson

Hello to all, I take the chance to send you a picture from a cupped oyster that I've found in European coasts. Here apparently, Crassostrea gigas has settled down and become invasive. But i've seen material from museum collections from the XIX belonging to Crassostrea gigas and they look quite different. I would appreciate some references for the original descriptions or diagnosis of Crassostrea gigas and other cupperd oysters to compare with and maybe some old works about the reproductive biology. Besides, any comment to the picture. Do Crassostrea gigas from its natural range look like this oyster? The older the references, the better, because there are some confusion about Crassostrea gigas and some authors consider Crassostrea angulata a synonym of C. gigas. 

Alexandra, they will presumably remain Crassostrea sp. until you will barcode them...but as a first step I would suggest to check for the absence of teeth near the hinge to confirm that at least they belong to Crassostrea.

Dear Fabio, thank you for the comment and tip. They belong to Crassostrea for sure. Close to the hinge the shell border seems smooth. Well, as to barcoding, considerimg that sometimes species uploaded to Genbank have been  misidentified and that there  are works that show hybridization among Crassostrea species, I don't think that barcoding solely will help in distinguishing among species. In any case my idea was to make an integrative approach combinig molecular data with morpholgical and biological data. But I need the original descriptions of the species and compare with material from the native range and previous to the cup oyster import and export during the XIX seculum. I send you attached a work of Dr Mariottini where it comes clear that barcode doesn't help much in certain situations. Previously there were also some problems with small oysters entering the Mediterranean. I send you in the next message the work published on PLOS ONE. I've to download it first. Best wishes

Here is the supplementary file to the article published in PLOS ONe. You see, C. gigas appear in two sister clades: one where there are only C. gigas and another in which C. gigas appear mixed with Crassostrea angulata. Unfortunately  there are no description nor figures of the vouchers, so it is difficult to assess what of the material was or was not realy c. angulata C, gigas or a hybrid. 

Thank you very much Dr.Alexandra and Dr.Fabio for your comments 

You will obtain nothing with original description and you should go on the type material (if still existing - angulata was described from Portugal if I remember well). However, angulata and gigas are cryptic species, so even if you will find the material you will not be able to assign it morphologically to any of the two, so you will only arrive to another end point. Therefore, from what we know, there are presumably two sister Crassostrea almost identical in Europe, to one the name angulata is given and to one the name gigas is given.  The only correct morphological identification for European Crassostrea is Crassostrea sp./spp.

Dear Fabio, thank you very much for your comments. Well, cryptic species as far as I know are species that cannot be distinguished morphologically, but there are researchers that are able to discriminate both combining a study of hybridization with morphometrical analysis. If you are interested in this work, I'm happy to give you the reference or to send you a copy in pdf. Let me know.

As to the neccessity of using material from the type locality to disentangle the "mischmasch", this was for me evident. I can get easily material from the type locality from C. angulata, or from where it is thought the type locality is, since apparently the type material is lost and as far as I know (or maybe I simply was no able to find the reference from where the type material is deposited and which is the type locality) nobody knows for sure where the type locality is. But to get fresh material from native, wild C. gigas is more difficult. For this, I need first to collaborate with people that know where to find wild C. gigas from the native range of distribution and from the type locality. And, you may admitt that to know the type locality of any species, you need to read the original description, where the type locality is indicated, right? Therefore, I would like to read the original descriptions. Besides, if for example a new combination shall be done with C. gigas and C. angulata and this new combination shall be described or if any of both specie shall be redescribed, you have to go back to the original descriptions as you must quote them, discuss them and justify your additions. So, saying that someone cannot obtain  anything from original descriptions is a statement upon which you should  think again more carefully. To the last, I invite you to continue the debate on Crassostrea and C. angulata privately, since maybe not all the researchers participating in the present forum will be interested in this subject. Best wishes

Crassostrea gigas was described from Japan. The description is here, free available to anyone: 

https://books.google.es/books?id=tMM4AAAAMAAJ&pg=PA140&hl=es#v=onepage&q&f=false

Unfortunately, the description can be referred to any possible Japanese oyster. That's why you need to go on type material, at least to see if it was a Crassostrea or something else (a Saccostrea? Another species of the several different genus within Ostreidae?). Then the real problems comes out. Because C. angulata was described from Portugal, but clearly comes from Asia as for almost all the Crassostrea, and so even if you will find the type material of C. gigas, you may be not able to assign it to any of the two species (or further ones). Because surely the type material is not in alcohol, it will be a destroyed empty shell. And therefore the loop comes out.

Best

F.

It is unfortunate that based on rather ill focused specimens of Oysters, the discussions are going a bit too far purely based on wild speculations. Concerning Crassostrea gigas/ Crassostrea angulata, following link could prove useful. Could it be Oyster shells? was the question asked.

http://www.europe-aliens.org/pdf/Crassostrea_gigas.pdf

Best

Syed

Henk:

You are probably right but identification of this "Coral Rock Oyster" purely based on morphology (ill focused in this case) could be tricky and difficult unless phylogenetic induced DNA sequence studies are undertaken (please see link):

http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0108696

Best

Syed

First, thank you Fabio for the link to the original description of Crassostrea gigas. Well, I will try to find somebody that knows Swedish to translate me the observations written by Thunberg. He wrote more than only diagnostic characters in Latin. Then, as to Dr. Jafar comment, in certain cases, I'm a bit suspicious about the power of molecular analyses to discriminate among closely related species, specially if cases of hybridization exist. In some cases, an integrative approach makes more sense combining molecular, morphological and biological characters. Independent lines of evidences should support species delimitation and also among species relationships, Thanks also for the link, I suppose it is the article from which I took the supplemantary file that I uploaded to the forum to show that not always molecular analyses are able to discriminate among oyster species. To find the proper genetic marker to discriminate among closely related species is sometimes very dificult.  

To the last, I attach the picture of an oyster that I collected long ago from Australia. Is this an Saccostrea oyster?

"New proceedings of the royal Swedish Academy of Science", Q2 1793.

Sub titled "Introduction to knowledge of WORMBEASTS in general, 4 class. Shells, Cochleata."

Translation of the text from Swedish of pp 140-142:

Drawing and description of a large type of Oyster from Japan;

by

C. P. Thunberg.

---------

On the coast of the Japanese Islands a kind Oyster is fished, that, mostly boiled, serves the islanders of this eastern Continent as food and is of the largest sort.

This kind of Oyster *) differs from others of its kin by the following distinctions and names [named properties?]: [note: following paragraph is in latin, someone else needs to translate that]

OSTREA gigas: testa rudi crassa oblonga lamellata; valvula inferiori subrostrata concave, superiori planiori breviori.

In size and weight it may vary, but mostly this one exceed all before known species, both in size, thickness and weight. Thickness reaches an inch, width a half qvarter [qvarter = 6 inches], length, as it varies with the age of the Oyster, is found to be from a half to a whole foot and weight is not seldom four or five skålpund. [slightly less than LB]

Shells are unremarkable, outside gray with several across lying wide scales and inside white and smooth.

Shells are unequal in size, particularly in the older, but always thick, as made up from separate leafs, whose number can be seen at the edges, rounded at the and and there whole.

Lower shell is at (cardo) locking pin [?] extruded to a blunt tip, domed and has a somewhat protruding edge.

Upper shell is shorter, and much flatter, seldom ridged [?]; in the elder it is fairly flat and smooth.

Animal size is in same proportion, as the length and thickness of the shell.

Tab. IV [List of three figures with 5 illustrations]

Fig. 1 shows outside of both shells, namely

a lower shell

b upper shell

Fig. 2 shows insides of both shells, namely

a lower shell

b upper shell

Fig. 3 shows a smaller younger oblong Oyster, closed to both its shells.

*): Found on my Journey to Japan 1775, and then named gigas; may be the O-ha of the Chinese (Osbeck p. 254) and the elongate of Museum. Florent.

-----

I guess the engraving was a foldout and the scanning didn't include folding out of diagrams. Being a 223 year old text, some of the words may have changed somewhat in meaning, but I believe the language is still pretty clear. The words with note or question marks (and others...) may have better English analogues for a specialist in the area.

Best regards,

Olof

Dear Olof,

great! Thank you so much for your translation! As I see, the colour of the native C. gigas's muscle scar must be completely white and the upper (right) valve in elder individuals flat. Currently, most cultured and invasive "C. gigas" have a muscle scar whose colour varies  from white to slightly violet. Best regards, Alexandra