Lineage analysis of micromere 4d, a super-phylotypic cell for Lophotrochozoa, in the leech Helobdella and the sludgeworm Tubifex

► We characterize the early progeny of the 4d lineage in the leech Helobdella. ► Each M teloblast makes 6 em cells which exhibit 5 distinct fates. ► These em clones provide all cells in the proboscis not accounted for previously. ► All teloblasts begin producing segmental founder cells at about the same time. ► The 4d lineage in the sludgeworm Tubifex also contributes non-segmental mesoderm.