The developmental timing of molting within the Ecdysozoa has diverged. In C. elegans, heterochronic mutants display retarded or precocious cell fates in relation to other developmental events, such as the larval molts. In contrast, heterochronic mutant phenotypes have not been reported in Drosophila, and the steroid hormone system involving ecdysone appears to have a central role in regulating developmental transitions. Which genes control molting in P. pacificus, and are these genes conserved with known molting regulators in C. elegans? Two P. pacificus molting-defective mutants emd-1 and emd-3 show stuck-in-molt phenotypes during all molts, including the embryonic molt inside the egg.