GENERAL HISTOLOGY

Detailed explanation-1: -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-2: -The madreporite is a sieve-like, calcified plate that connects the system to the aquatic environment. Water enters through the madreporite and flows through a tube, called the stone canal, that connects to the circular ring canal surrounding the mouth.

Detailed explanation-3: -Madreporite / sieve plate is the place where water is able enter the water vascular system; the ring canal takes the water to the radial canals; the radial canals take water to the ampulla and tube feet; the tube feet have many functions – movement, feeding, sensory, adhering to substrate, excretion & respiration.

Detailed explanation-4: -The madreporite is an essential part of the circulation system in echinoderms. Through this plate, which is also called a sieve plate, the echinoderm draws in seawater and expels water to fuel its vascular system. The madreporite functions like a trap door through which water can move in and out in a controlled manner.

Detailed explanation-5: -Most sea stars, sea urchins, and sea cucumbers have suction cups at the tips of their tube feet. In some sea stars and brittle stars the tube feet are shaped like little paddles. Water gets from the madreporite to the tube feet through the radial canal. Valves keep water from flowing back into the radial canal (Fig.