Water Vascular System of Sea Star (Echinodermata)

Water Vascular System of Sea Star 

Phylum: Echinodermata

B.Sc.F.Y.

Echinodemata group of animals the water vascular system is a divisional as a coelomic and distinctive features of sea star.

The water vascular system contains appendages of the body wall and its canals.

 It is also termed as ambulacral system. Since the entire system is derived from coelom, the canals are lined with a ciliated epithelium and filled with watery fluid. 

Water-vascular system functions as a means of locomotion. It consists of different parts such as madreporite or seive plate, stone canal, water ring or ring canal, radial canals and podia or tube feet present.

Echinodermata group of animals are different water vascular system are some what modified in different classes of the spacies.

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Asteroidea: water-vascular system

In asteroids, water-vascular system is based on the general echinoderm plan with certain modifications.

1. Madreporite:

Internal canals of the system connect with sea water outside through button-shaped madreporite or seive plate located on the aboral surface in interradial position. Seive plate is calcareous having numerous ridges and furrows. Furrow have about 200 pores, each of which leads into a pore canal. Pore canals join to form a common canal to open into an ampulla beneath the madreporite. Although a great majority of asteroids have but one madreporite. multiplication of madreporites is not rare.

2. Stone canal:

It is so named because of calcareous deposites located in its walls. 

S-shaped vertical stone canal are extended towards the world side of the animals body.

In the lumin of the stone can all are into two passages are divided by a longitudinal ridge.

In Henricia,the internal ridge very simple. 

In Asterias and Asterina, ridge is bifurcated into two rolled vertical lamellae. 

In Asteropecten, ridge meets the opposite wall dividing the interior into tubes provided with a pair of scrolls each. 

The lumen of stone canal is ciliated.

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3. Ring canal:

Stone canal opens into a circular ring canal or water ring situated just internal to the peristomial ring of ossicles around the mouth margin. 

Often the walls of the ring canal are folded to divide its lumen into a more or less separate channels.

4. Radial canals:

From the outer margin of ring canal are given out five radial canals. 

Each radial canal runs into each radial arm and terminates into the terminal tentacle at the tip of the arm. 

The radial canal runs on the oral side of ambulacral ossicles covering the ambulacral groove.

5. Lateral canals:

Each side of the radial canal, lateral canals are given off alternately which pass between the ossicles on cach side to enter the coelom. 

Ampulla connected to tube feet by a valve in each letter canal.

6. Polian vesicles:

On the outer side of the ring canal to form a five polian vesicles.

When sea star comes out side the water at that time to be utilised.

7. Tiedemann's bodies:

Tiedemann's bodies are in a five pairs in number it is a small irregular shaped of the body and there are present inner side of the ring canal.

Some forms have only 9 such bodies. 

Tiedemann's bodies are produc coelomic corpuscles and pass away into the ring canal such as the system is known as water-vascular system.

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8. Tube feet:

 A tube foot is a short hollow, thin,elastic walled closely located in the ambulacral groove. 

 Tip of the podium is flattened forming a sucker for attachment. 

Basal end of each podium pierces the ambulacral ossicle through a tiny ambulacral pore and expands to form a little rounded bulb called ampulla lying into the aboral side of the coelom. 

longitudinal and circular muscle fibres made by the wall of ampulla.longitudinal fibres only in tube feet and circular muscles is absent.

Four rows along the length of ambulacral groove has Podia are arranged .

 As lateral canal on each side are alternately long and short the podia look like in four rows instead of two. 

To row of Odia are present in lateral canal of the equal length only in some species.

Water-vascular system helps in locomotion. Animal moves by tube feet. 

Water entering the madreporite after passes into stone canal than ring canal then radial canal after podial canal and finally into goes to ampullae of podia. 

What are forcely in the tube food after the contract of ampulla and you feat is get elongated after filling of water.

Tip of the tube feet is like a sucker they are touches the substratum and contract again and again the water fluids goes back into the ampulla and body is run forward for the locomotion of the sea star..

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