Practice question

All animals share derived trait of extracellular matrix containing collagen particularly fibrillar and type IV network forming basal lamina underlying epithelia, providing tensile strength and polarity signals through integrin, laminin and proteoglycan interactions. No other kingdom synthesizes true collagen triple helix with hydroxyproline repeats in organized sheets. Additional shared characters include cadherin-mediated cell adhesion, tight and adherens junctions, Wnt β-catenin signaling, regulated caspase apoptosis and Hox patterning. Cell wall and photosynthesis belong Plantae, siliceous skeleton limited to particular sponges and diatoms not universal. Collagen matrix thus diagnostic metazoan synapomorphy.