This is a siphonophore.
Although a siphonophore appears to be a single organism, each specimen is actually a colony composed of many individual animals called zooids. Most colonies are long, thin, transparent pelagic floaters (meaning they normally exist neither close to the bottom or close to the shore).
Some siphonophores superficially resemble jellyfish. The best known species is the Portuguese man o’ war.
Researchers with the Nautilus Live expedition, a live-streamed deep sea exploratory mission, recently encountered a very rare specimen floating along the sea floor.
Check the footage: