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  • Canal System Of Sycon – Zoology Notes – For W.B.C.S. Examination.

    Sycon is a sedentary sponge. It leads an aquatic life. The body of sycon shows pores and canals which form a complex canal system. It is called sycon type of canal system. It is useful to draw water current inside the body. These water currents bring in food and oxygen.Continue Reading Canal System Of Sycon – Zoology Notes – For W.B.C.S. Examination.
     
    The body wall of sycon contains outer dermal layer and inner choanoderm. in between these two layer mesenchyme is present. The body wall is folded regularly and develop a regular canal system.
     
    1) Ostia: The body wall is folded. In between two folds an incurrent canal is present. The opening of incurrent canal shows a pore membrane. This will show one or two ostia, through which water enters into the incurrent canals. The ostium is surrounded by myocytes. These amoebocytes will work as sphincters. They can close these openings or open them to regulate the inflow of water.
     
    2) Incurrent canals: In between two folds of the body wall an incurrent canal is present. These canals end blindly towards inside. This is lined inside by pinacocytes. These are flat cells and are contractile.
     
    3) Prosopyles: The incurrent canal opens into the radial canal through prosopyles’.
     
    4) Radial canals: In between two incurrent canals a radial canal is present. It ends blindly to the exterior. It leads into excurrent canal internally. Radial canal is lined with choanocytes or flagellated cells. Hence these chambers are called flagellated chambers.
     
    5) Apopyle: Radial canal opens into excurrent canal through an opening called apopyle. The apopyle is also surrounded by Myocytes.
     
    6) Excurrent canal: It is short and wide chamber. It opens into spongocoel. This canal is lined with flat epithelial cell like the spongocoel. The board opening between excurrent canal and sponogocoel is also called internal ostium.
     
    7) Spongocoel: The central part of the cylinder of sycon will show a hollow cavity called spongocoel. it is lined with epithelial cells. At the apex it opens out through osculum.
     
    Because of the action of flagella of choanocytes water is drawn into the body. This is called incurrent water. This brings in food and oxygen. Hence it is called nutritive current. The water that goes out of the osculum is called excurrent water.
     
    Functions of Sponge Canal System:
    1. It brings constant supply of water into the body and helps in respiration.
    2. Water brings with in small food particles which are used by the sponge.
    3. It helps in the process of reproduction.
    4. It helps in the process of discarding waste matter out of the body.

    The water circulatory system of sponges also called as canal system is the characteristic feature of the phylum Porifera. Canal system is also known as aquiferous system. The canal system of sponges helps in food acquisition, respiratory gas exchange and also in excretion.

    The numerous perforations on the body surface of the sponges for ingression and egression of water current are the main constituents of the canal system. Inside the body, the water current flows through a certain system of spaces where by the food is captured from the incoming water and the excretory material is sent out into the outgoing water.

    Functions of the water current

    Water current plays the most vital role in the physiology of the sponges. The body wall of the sponges consists of two epitheloid layers the outer pinacoderm and the inner choanoderm. Pinacoderm consists of porocytes cells which bear openings called ostia. Choanoderm is composed of choanocytes or collar cells. The choanocytes have collar of microvilli around the flagellum. The water current is caused by beating of flagella of the collar cells. The following are the functions of the water current which enters the body of the sponges through the canal system:

    • All exchanges between sponge body and external medium are maintained by means of this current.
    • Food and oxygen are brought into body through this water current
    • Also the excreta are taken out of the body with the help of this water current.
    • The reproductive bodies are carried out and into the body of the sponges by the water current.

     

    Types of canal systems

    Different sponges have different arrangement and grades of complexity of internal channels and accordingly the canal system is been divided into the following three types:

     

    Ascon type of canal system

    This canal system is the simples of all the three. It is found in asconoid type of sponges like Leucosolenia and also in some of the developmental stages of all the syconoid sponges.

    The body surface of the asconoid type of sponges is pierced by a large number of minute openings called as incurrent pores or ostia. These pores are intracellular spaces within the tube like cells called porocytes. These pores extend radially into mesenchyme and open directly into the spongocoel.

    The spongocoel is the single largest spacious cavity in the body of the sponge. The spongocoel is lined by the flattened collar cells or choanocytes. Spongocoel opens outside through a narrow circular opening called as osculum located at the distal end and it is fringed with large monaxon spicules.

    The surrounding sea water enters the canal system through the ostia. The flow of the water is maintained by the beating of the flagella of the collar cells. The rate of water flow is slow as the large spongocoel contains much water which cannot be pumped out through a single osculum.

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