Distinguishing feature of Sponges is the perforation of body surface by numerous apertures for ingress and egress of water current.
Water current flows through a certain system of spaces collectively forming the canal system.
This water current maintains all exchange between sponge body and external system.
Food and oxygen are brought in, carbon dioxide and waste products are removed.
| Ascon Type Simplest type of canal system. e.g. Leucosolenia Ostia: Incurrent pores within tube like cells called Porocytes. Ostia open into the Spongocoel, which is a single, large, spacious cavity in the sponge body. Spongocoel is lined by flagellated collar cells or Choanocytes. Spongocoel opens to the outside through a narrow circular opening called the Osculum, located at the distal free end. Surrounding sea water enters the canal system through Ostia. Flow of water is maintained by beating of flagella. Flow of water is slow, because the large spongocoel contains much water that cannot be pushed out readily through a single Osculum. Ingressing Water — Ostia — Spongocoel — Osculum — Water Outside | |
| Sycon Type E.g. Scypha, Grantia Theoretically, it can be derived from Ascon by horizontal folding of walls. Embryonic development of Scypha shows the Asconoid pattern developing to Syconoid pattern. Two types of canals — incurrent and radial alternate with each other. Incurrent pores (Dermal Ostia) found on outer surface of body open into Prosopyles. Prosopyles open into Radial Canals, Radial canals open into Apopyles. Apopyles open into Spongocoel. Water from Spongocoel leaves outside through Osculum. Ingressing water — dermal Ostia — incurrent channels — prosopyles — radial canals — apostles — spongocoel — osculum — outside In more complex Sycon type (Grantia), incurrent canals are irregular, branching and anastomosing, forming large sub dermal spaces. | |
| Leucon Type Further folding of the body wall. e.g. Spongilla Radial symmetry is lost. Canal system becomes very irregular. The engrossing water comes into incurrent canals through Dermal Ostia. Passes through Prosopyles into Flagellated Chambers. Flagellated chambers communicate with excurrent canals through Apopyles. Excurrent canals are developed due to shrinkage of spongocoel. Develops directly without passing through Ascon or Sycon stages. Ingressing Water — Dermal Ostia — Incurrent Canals — Prosopyles — Flagellated Chambers — Apopyles — Excurrent Canals — Osculum — Outside | |
| Rhagon Type Spongocoel is surrounded by flagellated chambers opening into it through very wide apopyles. Canal system of Rhagon larva does not occur in any adult sponge. Leucon type can be derived from Rhagon. Ingressing Water — Dermal Ostia — Flagellated Chambers — Apopyles — Spongocoel — Osculum — Outside |