Question

Asconoid canal system occurs in
A. Grantia
B. Scypha
C. Leucosolenia
D. Spongilla

Answer 1

Hint: Asconoid sponges have the simplest organisational form. Tiny and tube-shaped, through dermal pores, water reaches the sponge and flows into the atrium. To remove it through a single osculum, Choanocyte flagella generates the current.

Complete answer:
The asconoid type of canal system is considered the simplest and most primitive type of canal system. In these sponges, the Asconoid type is present, whose body is vase-like and radially symmetrical. The wall is extraordinarily small. It encloses a wide spongocoel opening by a narrow osculum at the summit. There are choanocytes lining the spongocoel. Numerous microscopic apertures called the incurrent pores or ostia, which extend from the outer surface to the spongocoel, pierce the wall. Intracellular disposal of each pore in a porocyte. The presence of a complete continuous layer of choanocytes lining the spongocoel disrupted only by the porocyte is characterised by the asconoid form of the canal system.

It is the simplest type of canal system found in Leucosolenia-like asconoid sponges. It is the only canal system in which choanocytes are lined with spongocoel. Cells called porocytes are expressed by the ostia. Within them, these cells have an intracellular canal. The cells reach through the mesenchyme radially and open straight into the spongocoel. Grantia and Scypha have a canal system with syconoids, and Spongilla has a canal system with leuconoids. It also occurs in some freshly settled calcareous sponges like Clathrina in the Olynthus process.

Hence, the correct answer is (C) Leucosolenia.

Note: The beating of the flagella of choanocytes produces a steady water current. The flagella is not synchronously pounding, but individually pounding. The water current passes through the spongocoel directly through the ostia and goes out through an apical opening, the osculum.