pneumatophore

noun

1. A gas-filled sac or float of some colonial marine coelenterates, such as the Portuguese man-of-war.
2. An aerial root, in mangroves etc., specialized for gaseous exchange.
3. An apparatus consisting of a bag with a tube and mouthpiece, which may be attached to the body. The bag contains oxygen to be breathed by the wearer in rescue work in mines, etc.