Hardening of bio-silica in sponge spicules involves an aging process after its enzymatic polycondensation: Evidence for an aquaporin-mediated water absorption

► Sponges as a model system for evolution of metazoan body plans. ► Sponges as a model system for basic studies of skeleton formation in animals. ► Enzymatic polycondensation reaction for the formation of bio-silica. ► Expression of aquaporin gene for the first time shown during bio-silica formation. ► First description that bio-silica formation in animals requires a de-hydration step.