Manca (Armadillidium vulgare)

In Woodlice the juveniles that have just left the marsupium are called "Manca", probably derived from "something still missing".
A complete Woodlouse has 7 pairs of legs - one pair on each segment of the pereon, but in a manca the 7th segment is not yet fully developed (as seen in this image) and does not yet carry legs. It will need two moults to develop the 7th segment with fully functional legs.