Updated by: Arabinda Naik
1. Sycon is a sedentary sponge.
2. It leads an aquatic life.
3. The body of sycon shows pores and canals which form a complex canal system.
4. The water circulatory system of sponges also called as canal system is the characteristic feature of the phylum Porifera.
5. Canal system is also known as auriferous system.
6. The canal system of sponges helps in food acquisition, respiratory gas exchange and in excretion.
7. 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.
8. Inside the body, the water current flows through a certain system of spaces whereby the food is captured from the incoming water and the excretory material is sent out into the outgoing water.
9. 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.
10. The canal system is also responsible for regulating the sponge’s internal water balance and preventing the accumulation of surplus water. Some sponges have a simple canal system, but others have a system with several branching canals.
11. The organisation and complexity of the canal system are influenced by the feeding habits and ambient factors of the sponge.
12. The movement of water through the sponge’s canal system is propelled by ciliary activity and muscular contractions of the body.
13. Moreover, the canal system is essential for removing waste from the sponge’s body. All exchanges between sponge body and external medium are maintained by means of this current.
14. 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.
15. The reproductive cells are carried out and into the body of the sponges by the water current.
Ostia or dermal pores: The external grooves of body surface are covered by a thin pore membrane. It bears two or more openings, the ostia, or the dermal pores. These pores are surrounded by contractile myocytes. These can reduce the diameter of dermal pores and thus regulate the amount of incoming water. These open into the incurrent canals.
Incurrent canals: These are thin spaces located radially between adjacent radial canals that are similar in size and shape. They are surrounded by pinacocytes. They open to the exterior by ostia, but their interior ends are blind.
Prosopyles: Incurrent canals communicate with radial canals through prosopyles. Each prosopyle is a perforation in a single tubular cell, the porocyte.
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.
Apopyle: Radial canal opens into excurrent canal through an opening called apopyle. The apopyle is also surrounded by Myocytes.
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 spongocoels is also called internal ostium.
Spongocoel: It is the large central cavity into which the radial canals open through their apopyles. It is the central space all along the length of the body.
Osculum: The spongocoel opens to the outside through a terminal opening, the osculum. The osculum is surrounded by special contractile myocytes. These form a sphincter which regulates the rate of flow of water from the body. Water current plays the most vital role in the physiology of the sponges. The water current is caused by beating of flagella of the collar cells.
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.
Functions of the water current
1. Water current plays the most vital role in the physiology of the sponges.
2. The body wall of the sponges consists of two epitheloid layers the outer pinacoderm and the inner choanoderm.
3. Pinacoderm consists of porocytes cells which bear openings called ostia.
4. Choanoderm is composed of choanocytes or collar cells.
5. The choanocytes have collar of microvilli around the flagellum.
6. The water current is caused by beating of flagella of the collar cells.
7. All exchanges between sponge body and external medium are maintained by means of this current.
8. Food and oxygen are brought into body through this water current.
9. Also, the excreta are taken out of the body with the help of this water current.
10. The reproductive bodies are carried out and into the body of the sponges by the water current.
This canal system is the simples of all the three. It is found in asconoid type of sponges like Leucosolenia and in some of the developmental stages of all the syconoid sponges.
The asconoid type of canal system is re¬garded to be the most simple and primitive grade of canal system. Asconoid type is present in these sponges whose body is vase-like and radially symmetrical. The wall is extremely thin. It encloses a large spongocoel (atrium) opening at the summit by a narrow osculum. The spongocoel is lined by choanocytes. The body surface of the asconoid type of sponges is pierced by many 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.
Course of water current:
Ingressingwater → Ostia → Spongocoel → Osculum → outside
Occurrence:
This type of canal system is found in some simple adult calcareous sponges (Leucosolenia, Olynthus, Clathrina).
Physiology of water current production:
A constant water current is created by the beating of the flagella of choanocytes. The water current passes directly through the ostia into the spongocoel and goes out through an apical opening, the osculum.
Sycon type of canal system is more complex compared to the ascon type. The syconoid type of canal system represents the transitional grade between the simplest ascon type and more complex ones. The first step above the asconoid type of canal system is represented by the syconoid type of canal system.
The complication is due to the out-pushing of the wall into finger-like projections, called the radial canals, at regular intervals. In this type of canal system, choanocytes are only limited to the radial canals.
Simple sycon type:The simple type of canal system is found in the heterocoelous calcareous sponges typified by Sycetta. The radial canals are free projections of the wall without touching at any point and the external surface is composed of the blind outer ends of the radial canals. The incurrent canals have not definitely formed and the spaces between the radial canals serve as the dermal ostia. The radial tube is lined by flagellated cells, but the Spongocoel is lined by flattened pinacocyte cells.
Complex sycon type: This type of canal system is the characteristic of syconoid sponges like Scypha. Theoretically this canal system can be derived from asconoid type by horizontal folding of its walls. Body walls of syconoid sponges include two types of canals, the radial canals and the incurrent canals paralleling and alternating with each other. Both these canals blindly end into the body wall but are interconnected by minute pores. Incurrent pores also known as dermal ostia are found on the outer surface of the body. These incurrent pores open into incurrent canals. The incurrent canals are non-flagellated as they are lined by pinacocytes and not choanocytes. The incurrent canals leas into adjacent radial canals through the minute openings called prosopyles. On the other hand, radial canals are flagellated as they are lined by choanocytes. These canals open into the central spongocoel by internal ostia or apopyles. In sycon type of canal system, spongocoel is a narrow, non-flagellated cavity lined by pinacocytes. It opens to the exterior though an excurrent opening called osculum which is like that of the ascon type of canal system.
Sycon type with Cortex: Sycon canal system takes a more complex form in few species like Grantia, where the incurrent canals are irregular and branching forming large sub-dermal spaces. This is due to the development of cortex, involving pinacoderm and mesenchyme spreading over the entire outer surface of sponge. The walls of the radial canals fuse to generate tubular gaps (incurrent canals) that communicate with the environment via dermal ostia or dermal pores. Before reaching the outer ends of the radial canals, the incurrent canals take an uneven path throughout the cortex. Sometimes enormous irregular cortical spaces or sub-dermal spaces may be created..
1. Sponge Structure: Sycon-type sponges have a tubular or vase-like body structure, which is perforated with numerous tiny pores called ostia on the outer wall. These ostia serve as the entrances for water.
2. Collar Cells (Choanocytes): Inside the sponge's body wall, there are specialized cells known as collar cells or choanocytes. These cells have a collar of microvilli surrounding a flagellum, which extends into the central cavity of the sponge. The flagella of these cells are responsible for creating the water currents.
3. Water Ingestion: Water enters the sponge through the ostia due to external factors like water current or the sponge's own pumping action. The external pressure or the beating of flagella of neighboring choanocytes can help in drawing water in through the ostia.
4. Water Flow and Filtration: As water enters through the ostia, it flows into the central cavity of the sponge. The collar cells, with their beating flagella, create a current within the sponge. This water flow serves multiple purposes:
• Filter Feeding: Collar cells capture tiny plankton and particles present in the water, which are then ingested as food by the sponge.
• Respiration: Oxygen exchange occurs as water circulates through the sponge, allowing oxygen to diffuse into the cells and facilitating carbon dioxide removal.
• Waste Removal: Waste products generated by cellular metabolism are also carried away by the water current and expelled through a larger opening called the osculum.
5. Excurrent Flow: After the water has circulated through the sponge, it is expelled through the osculum, which is a larger opening located at the top of the sponge. The osculum acts as the exit point for the water, and this outflow maintains a continuous circulation of water.
6. Nutrient Uptake: As water passes through the choanocytes, the collar cells capture and digest small food particles, absorbing nutrients into the sponge's cells.
7. Nutrient Transport: Nutrients absorbed by the collar cells are transported to other cells within the sponge's body, where they are utilized for growth and various metabolic processes.
In this type of canal system, the choanocyte lining of radial canals evaginates into many small chambers which repeat the same process to give rise to a cluster of small, flagellated chambers. In many cases dermal pores open into subdermal spaces.
The subdermal space and incurrent canals lead into the small rounded flagellated chamber through an opening, termed as prosophyle. The flagellated chambers open by apopyles into excurrent canals which form large tubes. The largest one leads to osculum. Few gradations of leuconoid type of canal system are seen in sponges.
Eurypylous type:
In eurypylous canal system, the flagellated chambers lead into excurrent canals through wide apopyles. This is the simplest and the most primitive type of leuconoid canal system. In this type of the flagellated chambers directly communicate with the excurrent canal through broad apertures called the apopyles.
This type of canal system is seen in Plakina.
Aphodal type:
In apopyles instead of being wide opening are drawn into narrow canals. These canals are called aphodus. This connects the flagellated chambers with the excurrent canals. This type of canal system occurs in Geodia.
Diplodal type:
In this case both apopyles and prosopyles are drawn out into narrow canals called aphodus and prosodus. Example. Spongilla.
In Demospongiae, leuconoid condition is derived from the larval stage, called rhagon as found in Spongilla. The body is conical, and tent like in shape, tapering towards the osculum. The larval canal system includes flattened pyramid like form with broad base, called hypophare, a spacious spongocoel and a lateral wall, called spongophares. Flagellated chambers occur in each spongophare. The spongocoel is bordered by oval flagellated chambers opening into it by apopyles. Mesenchyme is considerably thick and is traversed by incurrent canals and subdermal cavity. Water enters the subdermal cavity through ostium and then enters the incurrent canal or it can be called prosodus. Flagellate chambers are connected to the spongocoel through the excurrent canal, or it can be called aphodus. This canal system is primitive as compared to diplodal type and when the larva grows transformed to diplodal type.The flow of water in asconoid canal system is Ingressing water → Dermal ostia → Prosopyles → Flagellated chamber → Apopyles → Sponocoael → Osculum → Outside.
The primary function of the Rhagon-type canal system, like all sponge canal systems, is to facilitate water circulation and filter-feeding. Sponges are filter feeders, which means they rely on the flow of water to obtain food and oxygen while expelling waste. The Rhagon-type canal system accomplishes this in several steps:
Water Inflow: Water is drawn into the atrium through small pores in the sponge's outer layer. The beating flagella of the choanocytes create water currents, causing water to flow from the atrium into the radial canals through the prosopyles.
Filter-Feeding: As water moves through the prosopyles and into the radial canals, choanocytes capture microscopic particles, such as bacteria and small organic particles, by using their collar cells. These captured particles are the primary food source for sponges.
Water Outflow: After passing through the choanocyte-lined canals, water exits the sponge through the apopyles, which lead back into the atrium. This unidirectional flow ensures efficient filtration and prevents the accumulation of waste within the sponge.
Gas Exchange: In addition to feeding, the flow of water through the Rhagon-type canal system facilitates gas exchange, allowing sponges to obtain oxygen from the water and release carbon dioxide.