Before starting this job I would have looked at this and seen nothing but a collection of pretty shells.
I mean, sure, I could have told you they were bivalves, in phylum Mollusca. I do have a degree in zoology. But I couldn’t have said whether these were the same species, or different, or what. In fact, what you see are representatives from three different families of clam: cockles, scallops, and arks.
Here they are seen from underneath, clockwise from the top left, with some helpful highlighting added by yours truly.
The trick to identifying them is to look not at the sizes and colors, which can vary, but at the hinge (the place where they would connect to their missing other halves). Cockles have a curvy indentation, scallops (yes, the same ones you order in seafood restaurants!) have triangular “ears” sticking out on either side, and arks are just straight across. Now the next time you go for a walk on the beach, you can wow your friends with your bivalve-identifying ability!