Moss vs. Spirogyra: Two plants enter, one has leaves

I don't know why this mattered so much, but during winter someone posted this photo of an alligator with plant matter on his back on Facebook, and said it was "moss" growing on its back.  I replied that it was pondweed, and the animal may have rolled in it.

He replied to say it was obviously moss as it was "hairy" and pondweed is "not hairy".

It was winter, so there wasn't much growth in my pond, but now it's spring, so here we go.

The stuff on the right is moss. Moss is famously not "hairy" - it's one of the most primitive plants to have proper leaves.  The stuff on the left is pondweed - this is the equally famous spirogyra of school microscope lessons fame - and it is by definition hairy, as it's made up of very long filaments.

In my case the spirogyra is being heaped up on the edge of a water flow, and lies in long, curly tangles.

The alligator photo was originally posted on Reddit, and you can read the thread about it here. The Redditors are interchangeably calling it "moss" and "algae" (algae is the plant type to which spirogyra belongs). They're not sure if the animal is sick and unable to clean itself, or growing the sweater, as they call it, or if it has rolled in it. Since alligators shed their scales like other reptiles, they should cast off any plant growth regularly. A few think it's the animal's ghillie suit, but I remain optimistic that alligators aren't that clever. I hope.

But whatevs, moss is not hairy.

He'll never see this, as that was on Facebook, and he's a friend of a friend anyway, i.e. someone I've never met and never will meet.  But, hey, picture of moss and pondweed.