The continuous deployment of the apical patterning system at larval and adult stages and the persistence of some
apical plate and organ cell types into post-metamorphic
stages would suggest that a gradual type of metamorphosis (where the bulk of tissues persist, see below) is
more ancient than the ‘catastrophic’ mode of metamorphosis dubbed maximal indirect development [19]. We
refer to such a biphasic life cycle, with gradual and limited
metamorphosis in which larval neural structures are incorporated into the adult nervous system, as ‘minimally
indirect development.’