Review articleThe polychaete-to-clitellate transition: An EvoDevo perspective

•The polychaete-to-clitellate transition was a major event in annelid evolution.•Direct development emerged in the clitellate lineage.•Pattern of cell fate segregation is conserved between polychaetes and clitellates.•A heterochronic shift between cell lineages results in direct development.•Modularity in axial patterning mechanism enabled the heterochronic change.