GENERAL HISTOLOGY

Detailed explanation-1: -Answer and Explanation: A. Water enters through the madreporite into the ring canal and from thence into the radial canals to the ampullae and finally into the tube feet. This shows the correct sequence of events.

Detailed explanation-2: -Water enters the system through the madreporite, flows through the stone canal, and enters the ring canal. A number of bulbous structures, called polian vesicles, that branch off of the ring canal serve as reservoirs to maintain extra water stores.

Detailed explanation-3: -The water vascular system is an important character in the echinoderms as the organisms reside in the aquatic environment. Water enters the vascular system through a structure known as madreporite. This is the structure through which echinoderms take in seawater and also expels the water outside the system.

Detailed explanation-4: -In sea stars, water enters the system through a sieve-like structure on the upper surface of the animal, called the madreporite. This overlies a small sac, or ampulla, connected to a duct termed the stone canal, which is, as its name implies, commonly lined with calcareous material.

Detailed explanation-5: -The water vascular system includes a circumoral canal (circular ambulacral or ring canal) situated around the mouth which gives tubular radial extensions, called radial canals. The number of the radial canals is usually five. But the number corresponds to the number of the radii of the body.