Starfish water vascular system PDF

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Starfish: Water vascular system Introduction The water vascular system is responsible for circulating water inside the body and performs so many vital functions. The water vascular system is a modified part of coelom and it consists of the certain corpuscles. It plays most vital role in the locomotion of the animals & comprises madreporite stone canal, ring canal, radial canal, Tiedman's body, lateral canals & tube feet.

(i) Madreporite: Madreporite is a porous button shaped structure. It is present in inter radial position. Madreporite contains about 200 minute pores .Each pore leads through pore canal. The pore canal unites to form a common canal that opens into an ampulae beneath the madreporite. (ii) Stone Canal: The stone canal is a vertical s-shaped canal that starts from the madreporite and extends orally and joins the ring canal. It is named stone canal because its walls are strengthened by hard calcareous rings. Its cavity is lined with flagellated or ciliated cells. The stone canal extends downwards (orally) and opens into a ring canal, around the mouth. In embryonic stages and in young Asterias, the stone canal remains a simple tube but in adult Asterias, the lumen of stone canal possesses a prominent ridge with two spirally rolled lamellae which by branching become more complicated in structure. (iii) Ring canal: The stone canal opens into a circular canal which is known as the ring canal. It is wide and pentagonal or five sided. Wall of ring canal are folded, dividing its lumen into more or less separate channels.

(iv)Tiedemann's bodies: The ring canal on its inner side gives off small irregularly shaped bodies which are known as the tiedemann’s bodies. They are of five pairs. The function of these bodies is to produce coelomic corpuscles which are released into the ring canal and so the system is known as water vascular system. (v) Polian vesicles: The ring canal gives off on its outer side five elongated pear shaped muscular sacs with long necks are known as the polian vesicles. These store water which is utilized when the star fish comes out of water. (vi) Radial canal: From its outer surface the ring canal gives off a radial water canal into each arm that runs throughout the length of the arm and terminates as the lumen of terminal tentacle. (vii) Lateral canals: In each arm the radial canal gives off two rows of numerous short narrow branches which are known as lateral canals. Each lateral canal is attached to the base of a tube foot and its provided with a valve to prevent backward flow of fluid into the radial canal. (vii) Tube feet: Tube feet is hollow, elastic, thin walled closed cylinder. The tip of podium is flattered forming a sucker for attachment. The basal end of the tube feet expands to form a little rounded bulb or bladder called ampullae. The ampullae have the same arrangement as the tube feed. Muscle fibers are present on walls of the ampullae and the tube feet. The lumens of the ampullae and tube feet are the continuation of the lateral canal. The tube feet are chief locomotory and respiratory organ of Asterias. Function of Water Vascular System :The water vascular system has three main functions. They are as follows1) Locomotion :- Starfish move using a water vascular system. When water comes into the system, it is then circulated from the stone canal to the ring canal and into the radial canals. The radial canals carry water to the ampulla portion of the tube feet. Each tube foot consists of an internal ampulla and an external podium When the ampulla is squeezed, it forces water into the podium. The tube feet latch on to surfaces and move in a wave, with one body section attaching to the surfaces as other releases. (2) Food Capture :- The tube feet are used to capture the prey. The suckers are used to open the shells of molluscas. (3) Attachment :- The Starfish can be attached to the rocks by the tube feet....