Types of Canal System of Porifera

The body of  the sponge is traversed by numerous canals opening to the outside by many minute pores. These canals and pores of Sponge constitute the canal system.

Types of Canal system :-  

There are four types of Canal system in Sponges. They are as follows-

(1)  Ascon Type :- 

It is the simplest type of Canal system. It is exhibited by sponges like Olynthus and Leucosolenia. These animals are cylindrical in shape. The body wall is formed of three layers, namely an outer ectoderm, a middle merenchyme & an inner choanocytes. The wall contains many pores called Ostia. These pores are intra-cellular because each pore is formed by the perforation of a single cell called Porocyte. All the ostia open into a central cavity called Spongocoel which is outside at the free end & by a large circular opening called Osculam. The beating of the flagella of the choanocytes creates a water current. The water flows in the following route.

Ostia → Spongocoel → Osculam

(2) Sycon Type :- 

The Sycon type of canal system is seen in sopnges like Sycon (Grantia), Sycetla etc. There are two types of sycon type canal system. They are- (a) Sycon type without Cortex (b) Sycon type with Cortex.

(A) Sycon Type without Cortex :- 

It is found in Sycetla. It is derived from the ascon type by the development of many finger- like, outgrowths on the surface. These finger like outgrowth on the surface. These finger like outgrowths are called Canals. These canals are lined with Choanocytes. But the spongocoel is lined with ectoderm. Between the radial canals there is another canal called incurrent canal. The incurrent canalsopen into the radial by minute pores canal Prosopyles. The radial canals open into spongocoel opening called apophles. The spongocoel opens outside by the Osculam. The water flows through the following route-

Incurrent canal →Prosopyle → Radial canal → Apopyle → Spongocoel → Osculam

(B) Sycon Type with Cortex :-  

This type is found in Sycon or Grantia. In addition to the previous type it has four additional features. They are as follows-

(i) The epidermis and Mesenchyme spread over the outer surface so as to form a cortex.

(ii) The free end of incurrent canals open to the outside by minute pores called dermal ostia.

(iii) The incurrent canal opens into the radial canal by openings called Prosopyles.

(iv) The radial canal opens into spongocoel by openings called apopyles.

In this type the water flows through the following route-

Dermal Ostia → Incurrent Canal → Prosopyle → Radial Canal → Apopyle → Spongocoel → Osculam