The three-dimensional architecture of the aquiferous systems of Spongia officinalis and Cliona viridis has been studied by corrosion cast analysis. The two species present similar multi-scale, modular canal arrangements. The incurrent systems consist of modular units with superficial small vessels, subsuperficial cavities, and ducts penetrating into the sponge body. Choanocyte chambers are distributed in clumps generated by modular, branched, small canals. Canals which drain the choanocyte chambers form an anastomosed framework which converges on large vessels leading to oscules. Some canals directly connect incurrent and excurrent systems, allowing water to bypass the choanocyte chambers. Comparison with previous sponge cast analysis of Petrosia ficiformis and Chondrosia reniformis reveals a basic anatomical design which could be widespread among demonsponges.