🌀o🌀! The chambered nautilus gets its name from the spiraling series of sealed rooms within its shell, each connected by the siphuncle, a specialized organ unique to shelled cephalopods that helps maintain the liquid/gas ballast within. Neutral buoyancy, positively amazing.
(Super quick nautilus PSA: One of the main threats facing nautiluses in the wild is harvest for souvenir shells. Nautiluses, unlike most cephalopods, can live a long time—20+ years—and reproduce very slowly. Please be well and skip the shell—don’t be naughty, save a nauti!)