The canal system in sponges develops from the folding of the inner wall (choanocyte layer). As the sponge body wall folds inward, it increases the surface area of choanocytes (collar cells) that line the canals and chambers, maximising water filtration and feeding efficiency. The three canal systems (asconoid, syconoid, leuconoid) represent increasing degrees of wall folding. The porous walls (ostia) allow water entry, but the canal system architecture itself results from inner wall folding.