Question

Simplest type of canal system is
A) Asconoid
B) Syconoid
C) Leuconoid
D) Rhagon type

Answer 1

Hint: The shell of all sponges is perforated by a wide number of openings through which water reaches the inside of the shell and flows into a series of criss-crossing canals that collectively shape the canal system, a distinctive characteristic of poriferans.

Complete Answer:
The canal system is the process of canals and chambers located in the phylum Porifera species. These canals are filled with choanocytes or collared flagellated cells. The canal system helps to add food and oxygen to the water circulating in the body.
Now, let us find the solution from the options-

A) Asconoid canal system: This is the simplest form of canal system present in Leucosolenia - like asconoid sponges. This is the only canal structure in which choanocytes are coated with spongocoel. Cells called podocytes are expressed by the ostia. Within them, these cells have an intracellular canal. The cells reach through the mesenchyme radially and spread directly into the spongocoel.

B) Syconoid canal system: Such type of canal system evolves due to horizontal folding of the asconoid body wall from the asconoid type. The pinacoderm lines the spongocoel, and the choanocytes are bound to tiny chambers named radial chambers. Incurrent canals are also there, in addition to radial chambers. Spongocoel is very small and extends through the osculum to the outside. Thus, option B is not the correct option.

C) Leuconoid canal system: This is the most intricate system of canals. Due to the folding of walls of radial canals, it evolves from the syconoid form. In leuconoid sponges, this form of canal system is found. The body's radial symmetry is disrupted, and the canal system therefore becomes very abnormal. The existence of excurrent canals is a characteristic function of this type of channel structure. Thus, option C is not the correct option.

D) The canal system type Rhagon is present in sponges of the Demospongiae family. During embryonic formation, this kind of canal system forms. Each chamber opens directly through a prosopyle at the body surface and through an apopyle into a spongocoel.

Thus, the correct answer is option (A) Asconoid.

Note: Water current that reaches the spongocoel through ostia is produced by the flagella of choanocytes. It brings nutrients and oxygen into the osculum and sweeps out metabolic waste. The canal system therefore plays the purpose of food collection, excretion, and respiration.