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.
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(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 canals open 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 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.
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.
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