Question

In sponges, incurrent canals are externally lined by
A. Choanocytes
B. Pinacocytes
C. Porocytes
D. None of the above

Answer 1

Hint: Sponges are multicellular organisms. Their body is full of pores and channels that allow circulation of water through them. Sponges are composed of unspecialized cells, these cells transform into other types. Unspecialized cells migrate between the mesophyll and main cell layers during transformation. Sponges lack digestive, circulatory, and nervous systems.

Complete answer:
-There are thousands of tiny pores present in the water canal system and the body surface of the sponges. With the flow of water through the tiny pores, the food particles enter the body.
Inside the body, the water current runs through a system of spaces and this constitutes the canal system.
The canal system is composed of an excurrent canal or a radial canal, an incurrent canal, and a prosophyle.
-Lining of the incurrent canals is by flat squamous cells called pinacocytes.
The function of pinacocytes is only to form water conducts and form a firm and smooth surface.
-Choanocytes line the internal chambers of sponges.
-Porocytes make up the pores of a sponge called Ostia.

Hence, the correct answer is option (B).

Additional information:
Pinacocytes are the flat cells that are present on the outermost layer of a sponge. The outermost layer is the pinacoderm. Pinacocytes also line the spongocoel. Pinacocytes maintain the structure and size of the sponge by slight expansions and contractions. These are of three types: Basic Pinacocytes, Endo Pinacocytes, and Exo Pinacocytes.

Note: The body of all sponges is penetrated by a large number of apertures by which water enters the body and water runs by a system of canals and this collectively forms a canal system. Incurrent canals are lined by pinacocytes in sponges. Pinacocytes maintain the structure and size of the sponge by slight expansions and contractions. These are T-shaped and have a nucleus in a cell body.