Question

Incurrent canals are lined by (a) Choanocytes (b) Pinacocytes (c) Porocytes (d) None of the above

Answer 1

Hint: Canal systems in the sponge body may be a system of characteristic crisscrossing canals (water channels) for water flow that communicates to the exterior through numerous apertures, the Ostia and osculum. It's a characteristic feature of poriferans.

Complete answer: The activities of the body of the sponges depend on the current of water entering through Ostia and passing out through the osculum or oscula. In sponges, the body wall is folded. In the midst of two folds, an incurrent canal is present. The opening of the incurrent canal shows a pore membrane. This may 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 will close these openings or open them to manage the inflow of water. In between two folds of the body wall, and the incurrent canal is present. These canals end blindly towards the inside . This is often lined inside by pinacocytes. These are flat cells and are contractile and lined by flat squamous cells and their functions are only to make water conduits and to make a little and firm surface. So the correct answer is ‘(b) Pinacocytes’.

Additional information:
The entire physiological activities of the animal depend upon the water current and therefore 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 an outsized number of Ostia is characteristic of Porifera.
Note: The body wall of sponges consists of two epithelioid layers, the outer pinacoderm and therefore the inner choanoderm. Pinacoderm consists of porocytes cells that bear openings called Ostia. Choanoderm consists of choanocytes cells or collar cells. The choanocytes have a collar of microvilli around the flagellum. The water current in sponges is caused by the beating of flagella of the collar cells.