The motus, these coralline islands of sand located on the reef crown of atolls or behind the volcanic islands' barrier reefs, are formed by the accumulation of sand in areas where the sea currents slow down (hoa's brink, rear reef, shoal). They can also be solely constituted of aggregates of calcareous concretions resting on a reef base. It is in these aggregates that the women looking for pupus, these tiny colored shells intended for the manufacture of necklaces, work.