A Larva Ballerina
Wikipedia explains, “A leptocephalus (meaning “slim head”) is the flat and transparent larva of the eel,.. Leptocephali (more than one leptocephalus) all have laterally compressed bodies that contain transparent jelly-like substances on the inside of the body and a thin layer of muscle on the outside. Their body organs are small, and this combination of features results in them being very transparent when they are alive.”
Never seen such a creature – such a delicate, rhythmic movement full of of easiness. Enjoy.