Can anybody please help with identification?

[lulu.shell]

Thank you Mikede for your confirmation, like Xbonet says, I bought them in a local supermarket in Spain, so this is where the confussion of origin might come from. On the box it said Atlántico, Portugal, but this may have just refered to the packager. Thank you so much for all your help, I have been trying to classify this bivalve for a few years now (ever since I bought the box at the supermarket).
Do you know, I lived in England for 11 years, in Cornwall, so right next to the beach, and never found a mercenaria? They look a bit like the gallina from Spain, only perhaps a bit bigger.
Have a nice weekend!

Gracias, Xbonet, efectivamente los compré en el Carrefour en una caja de 1 kG (?). Hace cosa de 5 años que intento averigüar cómo se llaman, y en el otro foro (aunque tal vez fuera por culpa de la foto), nadie pudo ofrecerme ninguna solución. Gracias por la confirmación! Buen fin de semana!