A student observes a worm-like organism crawling about on dead organic matter. Later, the organism sheds its outer covering. One possibility is that...

A student observes a worm-like organism crawling about on dead organic matter. Later, the organism sheds its outer covering. One possibility is that the organism is a larval insect (like a maggot). On the other hand, it might be a member of the phylum ______. One way to distinguish between the two possibilities is by looking for the presence of