Abstract
AbstractThis chapter deals with a number of topics not related to particular organ systems, but to the general body organization. These include: complexity (is there a constantly growing complexity during animal evolution?), size (can events of evolutionary size change be spotted?), symmetry (what are the basic symmetrical properties and what is their phylogenetic importance?), the anteroposterior axis (what is its significance for bilaterian evolution and did it predate Bilateria?), the dorsoventral axis (was there an inversion of this axis during metazoan evolution?), germ layers (what is the phylogenetic significance of germ layers?), segmentation (how often did segmentation and segmental patterns evolve?), skeletons (are skeletons phylogenetically informative?), locomotory appendages (are appendages comparable among animals?), and parasitism (what are the evolutionary changes in becoming parasitic?).
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