Swima

Swima is a genus of marine polychaete worms found in the ocean at depths between 1,800 and 3,700 meters (5,900 and 12,140 feet). Even if they are agile swimmers, they are often seen hanging immobile in the water column as they are neutrally buoyant. This deep ocean pelagic (free-swimming) genus has modified bioluminescent gills that can be cast off from an individual. These discarded gills somewhat resemble green "bombs" that remain illuminated for several seconds after they have been discarded. It is thought that this is a defensive mechanism rather than reproductive, as it is seen in both mature and juvenile individuals. And because they are eyeless, communicating with light would be difficult. Swima worms are closely related to the recently discovered genus Teuthidodrilus, another pelagic cirratuliform of the bathyal zone.