I found it on the floor after taking the engine out. It's about 3cm across.
And while I'm asking, what is the sensor revealed in the centreline in front of the radiator when you remove the front bumper?

 

Not sure what that is, but the sensor behind the front bumper is for outside temperature on the digital dash display

 

I can't recognize it either 😐 and Team and I have pulled a number of engines on these cars.

looks like a fiber flap or something that closes off a breather ...maybe for a vent on the tranny?

It's not likely an important part