Believe it to be this species, hiding in one of the only bushes above water level during a king tide. First mouse I've ever seen that didn't care that I was around. Didn't try to run away.
An extremely desiccated piece of something. Is it the organ of some animal, the dried pneumatocyst of some seaweed, or something else? Approximately 2" in diameter.
I added a bunch of algae from the small yard pond to a "Muckquarium" (a pond life aquarium that I keep) a couple weeks ago, and stirred it up a bit and moved some of it around last night, but this is the first time I've seen this. 🤯
I have no idea what it is yet, though it has six legs, so I'm assuming it is some kind of insect larva.
It is alive. I gave it a very gentle touch with a stick, and it twitched slightly, took a short video, where you can see that it's abdomen/tail seems to be pumping slightly. I'm guessing that it is pumping water through as it breathes.
Any ideas? Perhaps a dragonfly larva/nymph? 🤔
Update: It swims, and is quite quick. Quick enough that I was having trouble trying to get video of it with my phone.
Just going with the AI suggestion here. Please correct if needed.
The third photo is through a loupe at 5x. Very leathery and wouldn't tear.