ID: Hitchhiker clam & eggs(?) on glass.

[MKLKT]

So I've had this little hitchhiker clam growing slowly the last year or so, it's getting pretty big now (~1") but I'd like to know what species it is or at least family.



And for the last two weeks roughly every few days there appears to be an egg spawn placed on my front tank glass. I know it's happened separately because it clears off after a day or two and then is back in a different spot a few days later. Macro shots were too blurry but they have a solid white base with a clear sac hanging that shakes with the water movement. Guesses?



I have a huge variety of inverts but I know it's not ceriths at least.