That thing looks just like the muffler, just turned sideways! My muffler has the tailpipe coming from both cats going to the top of the muffler, then 2 u-shaped tubes that route back into the muffler. This one looks like one of the u-shaped tubes is routing to the back of the car...

I have a limited...and definitely nothing like that is under my car!

Maybe it's euro spec? Just a guess!

EDIT: I just checked the service manual...pages 11-11 and 11-12 describe what I have.