Modiolus mussels do occur worldwide. I am not aware of their being raised for food like Mytilus, though perhaps some species in some countries may be. Here in New England, the big mussel Modiolus modiolus is common, as well as the ribbed mussel Geukensia demissa, but no one eats either one of them, even though one Modiolus would provide 3 or 4 times as much "meat" as one Mytilus. The reason - they don't taste good. I have never actually tasted either one, but they do not enjoy the reputation for palatability that the Mytilus mussels do. Paul M. Rhode Island