For me it was this moth https://www.inaturalist.org/observations/5519433 , it still does not make sense to me.
I was down in New Orleans and we’d visited the grave yard that day, I remember the lightening bugs filling the night like second set of stars it was summer and the nights were humid and alive with unfamiliar sounds the air itself seemed to hum.
And then walking along the front porch I saw one of these male moths with those… tentacles extended and I wondered how I had crossed over into a world of demons and dark magic. Where even innocent ordinary moths could have this other form that was so unexpected and horrific.
It’s an amazing adaptation but… yeah.
For me, I was surprised by the Family Balanophoraceae. I’ve been fooled because intuitively I thought they were fungi but turns out they are plants!
I love lichens, but every time I try to learn more I have the “what the.. how was I supposed to even suspect that?” response.
Like there is one mentioned in the sonoran guide I just found that is often a mushroom, and occasionally it lichenizes in the middle? I’m sorry What?
For this year’s City Nature Challenge, I visited local preserves that I was pretty familiar with, and I was certain that I was not going to find anything extraordinary. I’m also self-taught and will never claim expertise in the slightest, but I thought I was pretty familiar with the local insect population, at least enough to give a general ID.
However, this year I managed to find https://www.inaturalist.org/observations/355815867 purely by chance (I don’t remember now what I was looking for when this caught my eye), which I had never seen before in my six years of visiting this location. I used Seek to help identify and gave my best guess, but apparently this is not a common species at all? And that’s only if my own guess was correct.
I just knew I was looking at something I’d never seen before at the time; it wasn’t so much the insect itself, but the fact I’d been here so many times and I’m STILL finding unexpected organisms is why A.) I keep going back, and B.) Why I think the CNC every year is so important. Without knowing the exact insect, I couldn’t guess if it was a beetle, shiny stinkbug or tick, or something else entirely.
(Other than this, every time I see a gastropod that is not a slug, my brain short-circuits.)
and then there’s the pink, which is An Other fungus ON the lichen
https://www.inaturalist.org/taxa/975913-Laetisaria-lichenicola
There’s Clathrus ruber (latticed stinkhorn, or as I think of it whiffle ball fungus). I saw a photograph of one which did make a convincing whiffle ball.
You might enjoy the series of videos from University of Florida IFAS extension, beginning with this one:
https://m.youtube.com/watch?v=fL6_hgaUGYw
I know I got a lot from their video on mosses. You can darken your phone screen and treat it like an audiobook, though occasionally you will realize you’re missing an important diagram, and need to rewind and actually watch a few seconds worth as video. Hope you enjoy.
Definitely these. The first time I found one, I felt sure I had found something extraordinary, not this very common non-native species. (And yes, insect larvae lovers of the world, I do know that they are remarkable!)
https://www.inaturalist.org/observations/370050994
Here’s another crazy lichenized one: https://www.inaturalist.org/observations/166413475
There’s a whole wikipedia page too: https://en.wikipedia.org/wiki/Basidiolichen
… is … is Elysia chlorotica a bit of a lichen? 
The concept is similar but it is not a fungi with a microbial “farm”/Partner. It uses kleptoplasty, stealing the chloroplasts.
Klepto like kleptomaniac, meaning stealing.
The last animal that really confused me was Harrisimemna trisignata. It’s a caterpillar that carries around shrunken heads but, plot twist, those are its own heads.
https://www.inaturalist.org/taxa/220974-Harrisimemna-trisignata
maybe it’s just nostalgic for its childhood… er… larvalhood.
I was so excited when I saw a bad-wing moth thinking it was my first emerald moth. It’s a little green geometer moth, what do you mean it’s not an emerald?!
Sorting kingdom disagreements can make you question whether you know anything about nature.
Recently I thought I was pretty familiar with marine life, especially with the marine life that lives in my local area. And then I discovered sea hares
More specifically, what I think was the carcass of a sea hare. Still, walking on the beach and finding something that looked vaguely like mis-colored chicken breast was really confusing (and kind of gross, respectfully).
Would you recognize Microdontinae larvae as being fly larva if you hadn’t seen one before? I’ve seen them mistaken for a gastropod a few times on here now. Larval forms can be so deceptive!
Soldierfly larvae definitely threw me when I first saw them, I was puzzling over whether they were isopods or beetles or something.
Then there was my first flea obs, which I thought was an auchenorrhynchan because, well, it was small and jumped a lot.
A more minor example was a Rhabdomastix cranefly I found, it had a wing venation abnormality that meant I ended up being confused over what kind of cranefly it even WAS for a long while.
Don’t these things mooch on ants and do fraud?