A bunch of stone canal is the characteristic of
Stone canal is characteristic of echinoderms. It is S-shaped. The stone canal extends downwards (orally) and opens into a ring canal, around the mouth. The walls of the stone canal are supported by a series of calcareous rings. The lumen of the stone canal is lined by very tall flagellated cells. It leads from the madreporite to the ring of the water-vascular system surrounding the mouth. So, the correct answer is option A.