The asconoid type of canal system is characterised by the presence of a complete continuous layer of choanocytes lining the spongocoel interrupted only by the porocyte (Fig. Each pore is intracellular disposed in a porocyte. The wall is pierced by numerous microscopic apertures termed as the incurrent pores or ostia which extend from the external surface to the spongocoel. It encloses a large spongocoel (atrium) opening at the summit by a narrow osculum.
Asconoid type is present in these sponges whose body is vase-like and radially symmetrical. The asconoid type of canal system is regarded to be the most simple and primitive grade of canal system. The following points highlight the three main types of canal system encountered in sponges.
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