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

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.

http://i.imgur.com/zgGawl.jpg

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?

http://i.imgur.com/TMNsHl.jpg

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

Nothin'? :p