it might have come off your spider, but it doesn't belong on your spider.
there are only 2 fuel hoses you undo to remove the plenum: one is the hose coming up to the injector rail (possibly someone put this aftermarket piece in there)
the other is the fuel return line from the pressure regulator, but why filter a return line...
Your spider has 2 original filters, a filter sock at the in-tank pump and the big main filter under the car near the main pump
(of course the tiny micro filter in each injector)
Perhaps it is what I have seen, and have heard called, an orifice tube (filter). It is used in the AC system. It is usually placed into the end of an AC hose, or the expansion valve. Perhaps it was replaced some time ago and the old one fell into the mess o wires and hoses above the intake manifold and has live there since, until you disturbed the area, and it fell to the floor. It is not from an injector, or any part of the fuel system, imo.