Tube
This hard cylinder, which varies in thickness between and even within species
of tubeworm, is basically like the shell of a lobster or crab. (Scientists call
it a "chitin proteoglycan/protein complex.") It grows as the worm grows,
providing a safe home for the animal. The delicate plume, which is the
tubeworm's only exposed part, can be retracted into the tube at a moment's
notice, such as when a hungry fish happens by, hoping to nibble the plume.
