Anyone Know What This Is?

I saw this on a (silk) leaf last night, never seen anything like it before, and it's gone now.  Looks like waste, but nothing in my tank is big enough to produce any poop this size, the "deposit" was about 8-9mm across.  Any ideas guys and gals?

It looks almost like a kid has been at the tank and sharing their breakfast cerio cerial with the fish. Otherwise not really sure what it could have been.

There's potential that you may have a large bristle worm in your tank. They can ingest sand, eat the organics and poop out just sand. 
 
I take it the bottom of the tank is sand? You'd be hard pushed to find the worm, probably buried under the sand and active at night. Shouldn't be much of a threat but some species are predatory. Probably does a good job of sifting the sand bed and keeping it clean. 
 
Try not to handle it if you find it as they are covered in fine hairs that can irritate your skin. 

Bristleworm?!  I'll keep a close watch!  Yes the bottom of my tank is sand, I made the change from gravel a couple of months ago.  Maybe I'm jumping to conclusions, but with you saying some are predatory could it explain the unexpected disappearance of a few juvenile (1/2 inch long) neon tetra?  All (remaining) fish and shrimp are fine and water is high quality and regularly tested and maintained.
 
Thanks!

Sometimes my tiger barbs will cruise the bottom of my tank, then spit sand as they swim upwards. Maybe your cory?

The corys sometimes scatter sand around through their gills as they swim upwards, but it's not the sand on the leaf that is the curious part; it was the pretty solid looking almost round thing!

Oh, THAT!! I wondered about that too, but thought it was some hifalutin' food you had! It looks like some sort of caterpillar. Weird!