It is often considered that early animals and their modern day representatives, sponges, lack polarity. This distinction is uncomfortable, because it is clear that the larva of a sponge (above) is highly polarized, and in fact polarity is necessary to coordinate swimming to a preferred site to settle. Some then say that only certain sponges (e.g. Calcarea and Homoscleromorphs) have polarity as adults. Are other adult sponges really unpolarized? What is polarity, why do animals have it, and how can we recognize it?
I am interested in the evolution of developmental genetic mechanisms that operate to pattern the early embryo, specifically the embryonic axis and certain types of polarity.