Box Jellyfish Chirp!
I always make sure to mention this at every chance I get, but a box jellyfish put into an ideal position (so this one, basically- it's the only one I've seen actually make this noise) will chirp
// ok, "whistle" is probably the most correct term in this situation since I believe the sound is just air coming out of the jelly's velarium (what water typically passes through when the jelly swims underwater)
but the sound is close enough to a chirp that I just call it that. It's cuter that way, imo



















