A spongocoel is the large, central cavity of sponges. Water enters the spongocoel through hundreds of tiny pores (Ostia

Ostium

Ostium may refer to:Anatomy*Ostium of Fallopian tube*Ostium primum or foramen ovale of the developing heart*Ostium maxillare of the maxillary sinus*Ostium of female lepidoptera genitalia...

) and exits through the larger opening (osculum

Osculum

The osculum is an excretory structure in the living sponge, a large opening to the outside through which the current of water exits after passing through the spongocoel. Wastes diffuse into the water and the water exits through the osculum at a velocity of nearly 8.4 cm/second, carrying away with...

). Depending on the body plan of the sponge (which can be asconoid

Asconoid

Asconoid is one of three possible body plans for sponges, which form the phylum Porifera in kingdom Animalia and subkingdom Parazoa which means that they do not have a definite body shape. The asconoid body plan is characterized by a stalk-like spongocoel surrounded by a single layer of choanocytes...

, syconoid, or leuconoid), the spongocoel could be a simple interior space of the sponge or a complexly branched inner structure. Regardless of body plan or class, the spongocoel is lined with choanocyte

Choanocyte

Choanocytes are cells that line the interior of Asconoid, syconoid and leuconoid body type sponges that contain a central flagellum surrounded by a collar of microvilli which are connected by a thin membrane. It is the closest family member to the free-living ancestor called choanoflagellate...

s, which have flagella that push water through the spongocoel, creating a current

Fluid dynamics

In physics, fluid dynamics is a sub-discipline of fluid mechanics that deals with fluid flow—the natural science of fluids in motion. It has several subdisciplines itself, including aerodynamics and hydrodynamics...

.