Question

The Choanocytes in a syncoid type of sponge are present in
A. Incurrent canals
B. Radial canals
C. Excurrent canals
D. Spongocoel

Answer 1

Hint: Choanocytes have the property to filter the particles out of the water by moving their flagella. In sponge, both respiratory and digestive functions are improved due to this feature of Choanocyte. In sponges, when sexual reproduction is required then Choanocytes convert into spermatocytes as sponges lack reproductive organs.

Complete answer:
The transitional grade system between the simple ascon type and more complex ones is called syncoid canal system in the sponge. The radial canals are the disturbances that occur because of pushing out of the wall into finger-like projections. In the body of sponges, radial canals are lined by the choanocytes or collar cells. They are small and chambers are flagellated.
In the body of sponges, the openings through which water enters from outside is called incurrent canals. Porocytes are the large conical peculiar cells that are present between pinacocytes in the pinacoderm and they look like an open tube. The incurrent canal is the sponge that is lined by the cells of the porocytes.
In the body of sponges, the openings through water flow out of the body is called excurrent canals.
The central cavity in the sponge body is called spongocoel. It opens outside the body through the osculum. There are hundreds of tiny spores called Ostia through which water enters the spongocoel and comes out from the osculum which is a large opening.
So, the correct answer is “Option B”.

Additional Information:
There are 2 types of syncoid canal system:
Simple sycon type – This canal system is found in calcareous sponges of heterocoelous.
Complex sycon type – This type of canal system is present in Scypha.
Sycon type with cortex – This type of canal system is found in various genera of calcareous sponges’ like Heteropia, Grantia, etc.

Note:
Thus, in the syncoid type of sponge radial canals are present which are surrounded by choanocytes. This simplest canal system in the sponge is of ascon type. The function of choanocytes in the sponge is critical. It helps in the water current generation through the sponge and is also used to trap and ingest the food particles by phagocytosis.