A late answer

Apologies for failing to post an answer for WIIW last night. Unfortunately our landline phone and hence internet was down.

Well this WIIW only attracted four guesses, three of them were biological in nature,

Linda G said “Fish gills?”

Christine said “Oh dear... Something on the side of a train?”
Which wasn’t a million miles away, but then she changed her mind, “But then on the other hand, it looks rather rubbery. Give in!”

Anne guessed, “I'm with Linda, although I'm going to say some kind of reptillian gills. Like on a lizard kind of thing. (Are they reptiles or amphibians?)”
I guess you mean something like an axolotl?

Well unfortunately the object in question is not at all biological except that it does have some  moss, and lichen growing on it. So no points for any of those answers.

Which brings us to Marcy who guessed “a vent perhaps?”

That is exactly right! 100%. No bonus points for guessing what it was on
.
I found this abandoned Toyota in the Toorongo River valley a couple of years ago. I just had to capture the contrast of the decaying equipment and the lush mountain river valley.

If you look closely you can see the vent on the side of the engine bay behind the front mudguard.