All in the Bauplan

This year is my last year teaching the Animal Form and Function dissection lab at the University of Ottawa.  I’ve done a lot for this lab over the years, and I want to do one more thing.

The course is a survey through the animal kingdom with a particular emphasis on body plans.  A creature’s “Bauplan” (in the original German) is the basic structure of its body, rid of peculiarities that disguise the similarity between the animal and its relatives.  The more deeply these plans are explored, the more the ancient relationships and divergences that link animals to the entire kingdom’s common ancestor can be illuminated.  Animal phyla, if the term still has any value, are often best understood as groups united by sharing a bauplan that distinguishes them from other groups, and these structures are important for an aspiring student of animal anatomy to recognize.

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All in the Bauplan
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Animal Form and Function 2: Mollusks

The next big chapter in the course I teach is on the mollusks.  The most visible component of any seashore’s biota, mollusks are an incredibly diverse group of animals.  One could be forgiven for not knowing in advance that snails, clams, and the colossal squid are about as close together on the tree of life as spiders and lobsters, or humans and pipefish.  Mollusks are, in this way, a classic example of adaptive radiation, in which an ancestral body plan somewhat like a very primitive snail was reshaped into widely dissimilar beasts in response to very different selection pressures.

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Animal Form and Function 2: Mollusks