Roj

The roj split from its ancestor, the ocean tristage. It is now completely mobile, pushing water through its center at high velocities to propel it through the water. On either side of the central cavity, tufts of fibre absorb any detritus and microbes that are caught in it. Using its fins to steer, and its ancestor's sensing fibres to create a map of its surroundings, it moves through the ocean in large, circular groups a single roj thick. It has also evolved the ability to produce and recieve minute amounts of electricity, allowing them to keep formation and respond to other's movements. The larger and older individuals are located near the center, with younger and smaller jetters occupying the rings as they move outward. The ones in the center will incubate the young in its central chamber until they find another of its kind, either one picked up from the sea by its parent, or another one of its siblings, where they attach, leave the parent, and enter formation. If the group is attacked, many of the smaller individuals will throw themselves at the predator, if not hurting it then confusing it long enough for the rest of the swarm to move away. The larger individuals are less likely to sacrifice themselves, allowing the swarm to keep its hierchal shape, though if to many accumulate in a single ring, they will split off and form their own swarm.