Based on
Figure 32.11, draw a phylogenetic tree of Bilateria that includes
the ten phyla of bilaterians discussed in detail in this chapter.
Label each branch that leads to a phylum with a C, H, HC, or N,
depending on whether members of the phylum have a coelom
only (C), hemocoel only (H), hemocoel and reduced coelom
(HC), or no body cavity (N). Use your labeled tree to answer
the following questions. (a) For each of the three major clades of
bilaterians, what (if anything) can be inferred about whether the
common ancestor of the clade had a coelom? (b) To what extent
has the presence of a coelom in animals changed over the course
of evolution?