Describe the canal system of sycon?

Answer 1

All the activities of their body of the sponges depend on the current of water entering through ostia and passing out through osculum or oscula. Inside the body, water current flows through system of spaces which collectively constitute the canal system. The entire physiological activities of the animal depend on the water current and the exchanges between the body and the exterior arc maintained through the water current. The food and oxygen are brought through this current while excreta and reproductive bodies are excluded through this current. The perforations of the body of the sponge by a large number of ostia is characteristic of phylum Porifera.

All the living tissues of the sponges are soft and it is a direct need of the animal to maintain a constant shape with different canals or passage-ways. Therefore, deeper layers of the body are provided with supporting spicules. Around the osculum, spicules are long and straight, while spicules situated around ostia are short and straight; around spongocoel they are T-shaped, while triradiate in the body-wall.

Thus, all the cavities of sponges with intricate passages of canals, traversed by currents of water entering by pores and passing out by osculum are collectively termed as a canal system of sponges.

A typical canal system is composed by following components :

(a) Incurrent canal - It opens externally to the outside by a small pore known as incurrent pore or ostium, but internally it ends blindly.

(b) Radial canal or excurrent canal- It is closed externally but opens internally by minute pores or apopyles into a central cavity or cloacal cavity or gastral cavity or spongocoel, which cannot be compared in any way with the stomach or intestine of other animals.

(c) Prosopyle- It is a smaller canal or passage-way connecting incurrent canal with radial canal.

The incurrent canals are lined by flat squamous cells and their functions are only to form water conduits and to form a smooth and firm surface.

The radial canals are lined by collar cells opening at the surface and are provided with flagella or whips. The lashing movements of flagellum procure the food particles and push them into the cell-mouth. Thus, this is food-capturing arrangement of sponges.

Spongocoel or cavity is lined by a thin gastric epithelium. It opens to the outside by an aperture, called osculum.

The arrangement, and complexity of the canal system varies considerably in different sponges and has been divided into four types :

1. Ascon type

2. Sycon type

3. Rhagon type

4. Leucon type