Question

In most simple type of canal system of Porifera, water flows through which one of the following ways?

• A. Ostia $\to$ Spongocoel $\to$ Osculum $\to$ Exterior
• B. Spongocoel $\to$ Ostia $\to$ Osculum Exterior
• C. Osculum $\to$ Spongocoel $\to$ Ostia $\to$ Exterior
• D. Osculum $\to$ Ostia $\to$ Spongocoel $\to$ Exterior

Answer 1

The correct option is A Ostia $\to$ Spongocoel $\to$ Osculum $\to$ Exterior

In the simplest type of canal system, the ascon system, water enters through intracellular pores ostia into the central canal called as spongocoel and exists through large central opening of spongocoel, the osculum. This makes option A correct.

Option B is incorrect as water enters through ostia in spongocoel, vice versa is not true.

Option C and D are incorrect as simple type of poriferan canal system has osculum as exit opening; water cannot enter through osculum but is always expelled out through it.