Compare Asconoid, Syconoid, And Leuconoid Canal Systems

These three systems represent an increase in the complexity and efficiency of the sponge's body plan, moving from a simple bag to a complex network.

• Asconoid: This is the simplest and least common system, found only in small, tube-shaped sponges. It consists of a central cavity called a spongocoel that is lined with choanocytes (collar cells). Water enters through tiny pores (ostia) that pass directly through the body wall into the spongocoel, and then exits through a single large opening, the osculum.
• Syconoid: This is a more complex, folded version. Water enters through ostia into incurrent canals. From there, it passes through small pores (prosopyles) into radial canals. These radial canals, not the spongocoel, are lined with choanocytes. The water then exits the radial canals (via apopyles) into the spongocoel, which acts as a central exit channel, before leaving through the osculum.
• Leuconoid: This is the most complex and most common system, found in the largest sponges. The body wall is thick and contains a highly branched network of canals. Water enters via ostia into incurrent canals, which lead to numerous small, discrete flagellated chambers. These chambers are lined with choanocytes. Water exits these chambers (via apopyles) into excurrent canals, which join to form larger canals that eventually lead to one or more oscula. There is no large, central spongocoel.