Considered some of the longest animals in the world, the Siphonophores are impeccable creatures of the deep sea. Observing them underwater, you may be illuded into thinking they're a string of fireworks - they are known to emit red fluorescent light, which scientists believe is uncommon in deep-sea creatures.
Although bioluminescence is often utilized by bioluminescent creatures as a tool to evade and escape predators, the Siphonophores seem to be using them to capture prey - an interesting twist on the norm of sea creatures. Younger Siphonophores have been observed to emit the standard blue light - a color that keeps predators away. However, scientists speculate that as the Siphonophores age, fluorescent compounds begin to cover the blue light-emitting spots, absorbing the glow and re-emitting it as red instead. The red is thought to be reflective of copepods (tiny relatives of shrimps) which are the preferred meal of some deep-sea fish. Because of this, it is suggested that Siphonophores bait prey using their bioluminescence, instead of trying to escape predators. When disturbed, they tend to glow green or blue.
Now that we've introduced perhaps the most interesting thing about Siphonophores, what are they and what do they look like?
Underwater, they appear to be a string of fireworks; a singular creature. Upon closer inspection, they are not individual organisms. Rather, they are colonies comprised of medusoids and polyploid zooids that are specialized. Zooids are considered multicellular organisms that develop from a single fertilized egg, and combine to create colonies that are able to reproduce, digest, float, maintain body positioning, and use jet propulsion to move. As seen in the picture, most colonies are long, thin, transparent floaters. They can reach up to lengths of 40 meters or more, longer than a blue whale. Because of this, they are considered one of the longest animals in the world. Siphonophores are gelatinous, and most of them disintegrate when sampled with nets. They reproduce asexually through a budding process, building up the colonies. A single bud is referred to as the pro-bud, which initiates the growth of a colony by undergoing fission.
Like jellyfish, Siphonophores can sting with their tentacles, which comprise colonies of stinging nematocytes. Nematocytes are referred to as "hollow harpoons that shoot out on contact, injecting venom and hooking prey". Even worse than jellyfish, these colonies can break loose from the overall organism, and still do immense damage whilst floating around on their own. The most excruciating sting is considered to be that of the Portuguese man o' war, which may cause unbearable pain for humans. Even the Siphonophores that wash ashore can deliver a sting. However, their stings are not deemed deadly.
When these colonies are separated from one another, they cannot truly survive - despite being able to deliver stings whilst floating around. Although they look eerily beautiful and captivating, you might want to keep your distance...