Sponges have a particular body plan with a pore/canal system that is arranged into one of three types: asconoid, syconoid or leuconoid. Asconoid sponges have the simplest organization consisting of a porous tube shape, an osculum, and an open internal area (spongocoel) that is lined with choanocytes. Syconoid sponges are larger and more complex than asconoid sponges. They have a thicker body wall and elongated pores that form a simple canal system. Leuconoid sponges are the most complex and largest of the three types. They have an intricate canal system with several chambers lined with flagellated choanocytes that direct water flows through the chambers and eventually out the osculum.