Q.3 What is canal system? Explain the mechanism and importance of water circulation in sycon. (2006)
Related Question -
Q. Give an illustrated account of the canal system found in porifera. (2008)
Q. Give an account of canal system in porifera. (2019)
Q. Give a detailed account of canal system in Sycon and its significance. (2010, 2011)
Q. Write short note on Porifera canal system. (2013, 14)
Ans. Water current plays a vital role in the physiology of sponges. All the exchanges between the sponge body and external medium are maintained by means of this current. Food and oxygen are brought into the body and excreta and reproductive bodies carried out. This current is caused by the beating of the flagella of the collar cells. A distinguishing feature of all the sponges is the perforation of the body surface by numerous ostia. Inside the body the water current flows through a certain system ofspaces collectively forming the canal system.
The arrangement and complexity of the internal channels vary considerably in different sponges. Accordingly the canal system has been divided into three types-ascon,sycon and leucon.
(1) ASCON TYPE: -
It is mainly found in leucosolenia. The body surface is pierced by a large number of minute openings called incurrent pores or ostia. These pores are spaces within the tube-like cells the porocytes which extend radially into the mesenchyme and lead into the spongocoel. This is a single, large spacious and central cavity in the sponge body and is lined by the flagellated choanocytes. The spongocoel opens to outside through a narrow circular opening the osculum which is often fringed with large monaxon spicules.
Into the canal system flows the surrounding sea water. The flow of water is maintained by the beating of the flagella of collar cells. The rate of water flow is slow, because the large spongocoel contains much water which cannot be pushed out readily through a single osculum. This is the course of water fow -
Incoming water - ostia - spongocoel - osculum - outside.
(2) SYCON TYPE: -
It is a more complex system of pores and canals and is characteristic of syconoid sponges like scypha(sycon). It is derived from ascon type. The syconoid arrangement is such that the body wall includes two types of radiating canals incurrent and radial paralleling and alternating with each other. The incurrent porees or dermal ostia found on the outer surface of the body opens into the incurrent canals. These canals are non-flagellated as they are lined by the pinacocytes and lead into the radial canals through openings the prosopyles. The radial canals are flagellated chambers, as they are lined by choanocytes. These canals open into the spongocoel by internal ostia or apopyles. The spongocoel is a narrow, non flagellated cavity that opens to exterior through an excurrent pore, the osculum similar to that of ascon type. The course of water flow is as follows -
Incoming water - dermal ostia - incurren canals - prosopyles - radial canals - apopyles - spongocoel - osculum - outside.
In still more complex type as illustrated by Grantia the incurrent canals are irregular, branching forming large sub-dermal spaces.
(3) LEUCON TYPE: -
As a result of the further folding of the body wall the sycon type gives rise to a still more complex canal system the leucon type as in Spongilla. The flagellated chambers are small and spherical cavities lined by choanocytes. The incurrent canals open into these chambers through prosopyles and the flagellated chambers in their turn communicate with the excurrent canals are developed as a result of the shrinkage and division of the spongocoel. The excurrent canals communicate with the outside through an osculum. The flow of water is as follows -
Incoming water - dermal ostia - incurrent canals - prosopyles - flagellated chambers - apopyles - excurrent canals - osculum - outside.
Through the leucon type of canal system appears to be the modification of the sycon type, in many calcareous sponges the leucon type is developed directly without passing through ascon and sycon types in their embryogeny.
In Desmospongiae the leuconoid condition is derived from a larval stage called the Rhagon type. Its spongocoel is surrounded by the flagellated chambers opening into it through very wide apoppyles. A single osculum opens at the top of the spongocoel. The canal system of rhagon larva does not occur in any adult form. Because of its derivation from rhagon stage in desmospongiae the leucon type of canal system is also termed as the rhagon type.
The leucon type of canal system presents three successive grades in its evolutionary pattern.
(a) Eurypylous Type: -
It is most primitive type of the leucon type of canal system. In this type the flagellated chambers communicate by broad apertures the apopyles, with the excurrent canals. For eg.Plakina.
(b) Aphodal Type: -
In several leuconoid sponges like Geodia the apopyle of the eurypylous type is drawn out as a narrow canal called aphodus. This connects the flagellated chamber with the excurrent canal.
(c) Diplodal Type: -
In some sponges like Oscarella besides aphodus another narrow tube called prosodus is present between the incurrent canal and the flagellated chamber. The pattern is called the plodal type.
Q.4. Draw well labelled diagram of the canal system of sycon. Discuss the importance of canal system in sponges. (2016)
Ans. Canal System of Sycon type: -
It is a more complex system of pores and canals and is characteristic of syconoid sponges like scypha(sycon). It is derived from ascon type. The syconoid arrangement is such that the body wall includes two types of radiating canals incurrent and radial paralleling and alternating with each other. The incurrent pores or dermal ostia found on the outer surface of the body opens into the incurrent canals. These canals are non-flagellated as they are lined by the pinacocytes and lead into the radial canals through openings the prosopyles. The radial canals are flagellated chambers, as they are lined by choanocytes. These canals open into the spongocoel by internalostia or apopyles. The spongocoel is a narrow, non flagellated cavity that opens to exterior through an excurrent pore, the osculum similar to that of ascon type. The course of water flow is as follows -
Incoming water - dermal ostia - incurrent canals - prosopyles - radial canals - apopyles - spongocoel - osculum - outside.
In still more complex type as illustrated by Grantia the incurrent canals are irregular, branching forming large sub-dermal spaces.
Importance of Canal system in Sponges: -
Significance of Canal System: -
Significance of: canal system in sponges is as follows :
1. The canal system serves the purpose of nutrition. It is regarded as a highway for the food through the body cells in the radial canal with flagella, which capture the food particles. Water currents are poduced by flagella, thus, waters flows into the central cavity or spongocoel. Smaller food particles e.g. diatoms,
protozoa and particles of organic debris are ingested into the cells protoplasm and digested.
2. In sponges as a result of development of canal system massive growth is found.
3. Streaming currents of water have dissolved air therefore, gaseous exchange or respiration takes place in the cells. Oxygen is taken in by simple process of diffusion and CO2 is given out.
4. Canal system also helps in excretion. Current of water, which pass outside the osculum remove the carbonic acid and other nitrogenous waste substances which are excretory products of the body.
5. The purpose of the canal system is also to increase the surface area of the animal in water.