The origin of moulting in animals

Publication by the LGL-TPE in Proceedings of the Royal Society B on July 10, 2019. Abstract: Millions of crustaceans, insects, myriapods (millipedes), chelicerates (spiders, scorpions) and worms, have an inextensible external skeleton and have to grow through successive moults during their lifetime. They belong to the supergroup Ecdysozoa. The moulting process (ecdysis) is strictly controlled by the endocrine system and allows these animals to grow in size by periodically renewing their cuticle. The lowermost Cambrian fossils from China described here show that this complex process appeared during the early stages of animal evolution, at least 535 million years ago, as evidenced by remarkably well-preserved moults of marine worms. Microscopic and microtomographic show that these ornamented worms moulted in a manner similar to that of extant priapulid worms, extricating themselves smoothly from their old tubular cuticle or turning their exuviae inside out like the finger of a glove. This is the oldest record of moulting in ecdysozoans.