This video from CreatureCast.org shows a Siphonophore. Technically, it is a colony of Siphonophora. The Jellies Zone says some siphonophores can form chains over 100 feet long. CreatureCast explains that the jellyfish like creature seen below is actually a colony of organisms.
What looks like one long body in this video is actually a free-swimming colony of clones — many genetically identical bodies that are all attached. But each body in the group isn't just like its neighbor. They each do a specific job for the colony. Some individuals will swim, some will catch food, and some will reproduce.
You can see a couple other interesting videos of Siphonophores here and here.
