We have studied the textures of lamellar phases of lyotropic systems in the sponge-lamellar domain of coexistence. The typical defects of the smectic systems (focal conics domains or "FCDs") are present, but our observations show also the existence of surfaces on which the director is discontinuous at optical scales. We have interpreted those surfaces as curvature walls. After having given their main geometric and energetic properties, we examine different cases (static and dynamic) which illustrate the importance of curvature walls in the formation of the lamellar textures.