The vaterite cover on the eggs of Anhinga anhinga and its effect on gas conductance (Aves: Anhingidae)



The nature of the chalky cover of Anhinga eggshells and its effect on gas conductance were studied. The cover consisted of microscopic spheres of nearly pure CaCO3 in the form of vaterite. The pore canals were unbranched with an inorganic cap (Board's type 3(a) (ii)). The cover acted as a resistance in series with the underlying calcitic shell and accounted for approximately 6% of the total conductance.