This organism appeared from some groups of marollons, when these had decided to leave the vent environment to venture into flatter waters, also searching for protection against the attacks of the snowky. Despite the marollons digging of holes, part of them remained displayed and the snowky was capable of capturing it. With this migration, its body became soft and long, sometimes growing to five times the size of its ancestor, in virtue not to be more sensible to the vents' environmental conditions.
There, as well as its ancestor, it digs a hole in the sand, but remains there for all its life. In the beginning of its life, it remains completely buried, feeding only on water microorganisms. During this phase, its shell becomes thicker and covers all its body and, after a certain moment, the shell is untied from the animal's body, which remains in its interior. From this moment, the trapinout is capable of capturing larger prey through its exclusive tactics of hunting.
Its name, "trap-in-out", come from the fact that it creates a trap in the deep of the sea, where it hides itself. With its paddles, atrophied with the passing of the time, it makes wavy movements in order to attract the attention of the nearest animals, always keeping its head in the interior of the shell. When the prey starts to pursue the false worms, the paddles of the trapinout begin to enter into the hole, forcing the animal to follow them while the trapinout starts to leave its shell in the other extremity. Its tentacle-like structure had developed a type of immobilizing poison that is launched onto the victim at the moment of the attack. The food is then captured once next to the hole and is brought next to the shell, remaining there until it can be totally consumed.