Types of Canal System of Porifera

(3) Rhagon Type :- 

This type of canal system is found in Rhagon which is the larval form of Spongilla. The Rhagon is conical in shape. It is broad at the base and pointed at the apex. Here the radial canal is in the form of rounded chambers called Flagellated Chambers. The flagellated chambers open to the outside by dermal ostia or Prosopyles and they open into the spongocoel by opening called apopyles. The spongocoel opens to the outside by the osculam. The water current takes the following route.

Dermal Ostia → Prosopyle → Flagellated Chamber → Apopyles → Spongocoel → Osculam.

(4) Leucon Type :- 

The Leucon type of canal system is derived from the Rhagon type. The Leucon type has following advanced characters.

(i) The dermal Ostia open into subdermal spaces.

(ii) The subdermal space open into Incurrent canals.

(iii) The incurrent canals open into Flagellated Chambers.

(iv) Choanocytes are located only in flagellated chambers.

(v) The flagellated chamber leads into excurrent canals.

(vi) The excurrent canals open into Spongocoel.

(vii) The Spongocoel opens to the outside by an Osculam.

There are three kinds of Leucon type of canal system followings-

(a) Euryphylous Type (b) Aphodal Type (c) Diphodal

(a) Euryphylous Type :- 

This type of canal system is exhibited by Telilla, Plakortis etc. This type has the following features :-

(i) The incurrent canal opens into the flagellated chambers by openings called Prosopyles.

(ii) The flagellated chambers are arranged in dusture.

(iii) The flagellated chambers open into the excurrent canal by openings called Apopyles.

(iv) The current of water takes the following route :

Dermal Pores → Subdermal Spaces → Incurrent Canal → Prosopyles → Flagellated Chamber → Apopyles → Excurrent Canal → Spongocoel → Osculam

(b) Aphodal Type :-

The aphodal type of canal system is seen in Geodia and Stelleta. It has the following salient features :-

(i) The flagellated Chamber opens into excurrent canal through a canal called Aphodus.

(ii) The water current takes the following route :

Dermal Ostia → Subdermal Spaces → Incurrent Canal → Prosopyles → Flagellated Chamber → Aphodus → Excurrent Canal → Spongocoel Osculam.

(c) Diphodal :- 

This type of canal system is seen in Spongilla, Oscarella etc. In this type the incurrent canal opens into the flagellated chamber through a canal called Prosodus. The water current flows through the following route :-

Dermal Ostia → Subdermal Spaces → Incurrent Canal → Prosopyles → Flagellated Chamber → Aphodus → Excurrent Canal → Spongocoel → Osculam

Function of Canal System :-

The canal system creates a water current to flow in & out of the Sponges continuously. This water current has the following functions :-

(a) Respiration :- 

The cells absorb O2 from the water current & gives out CO2.

(b) Nutrition :-

The water current brings in food particles.

(c) Excretion :- 

Nitrogenous waste products & faeces are washed out by the water current.

(d) Reproduction :- 

The water current carries the sperms from one sponge to another sponge.