Zoology 10th Edition by Stephen Miller,John Harley

Exercise 3

Ecdysozan phyla are united by molecular characteristics and the presence of a nonliving cuticle that is molted during growth. Ecdysoza is composed of eight phyla: Nematoda, Nematomorpha, Kinorhyncha, Priapulida, Loricifera, Arthropoda, Tardigrada, and Onycophora. The latter three comprise a clade called Panarthropoda. The cuticle of arthropods is their exoskeleton, and in pseudocoelmate ecdysozoans, it aids in the function of the pseudocoelom as a hydrostatic skeleton.
What morphological feature unites all members of the clade Ecdysozoa?