The siphonophores are an order of marine animals in the phylum Cnidaria (the same phylum containing jellyfish). There are about 200 different species of siphonophores known.
Although they superficially resemble jellyfish, each siphonophore animal is actually a colony of many genetically identical individuals called zooids.
Each zooid is specialized to serve a particular function (such as swimming, feeding, prey capture of reproduction) within the colony—so much so that individual zooids cannot survive alone.
The infamous and venomous Portuguese man o' war is a member of this order. It lives at the water’s surface, trawling the depths for suitable prey with its long tentacles.
Most siphonophores live in the deep ocean where there is no light other than the light emitted by organisms. Even some siphonophores can emit light. A species in the Erenna genus found off the coast of Monterey, California has stinging cells that glow red, probably to attract the small fish upon which it preys.
This species is only the second life form known to produce a red light, the first being the scaleless dragonfish (Chirostomias pliopterus).
Siphonophore (2017-09-22) by NOAAOriginal Source: NOAA Office of Ocean Exploration and Research, Deep-Sea Symphony: Exploring the Musicians Seamounts