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Water Vascular or Ambulacral System of Star Fish ; Asterias

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 Water Vascular or Ambulacral System

  • Water Vascular System is a unique feature of  of all the echinoderms which helps mainly in locomotion. 
  • This it is the modified part of the coelom and consists of a system canals which is filled with sea water, containing amoeboid corpuscles. 
  • It plays a vital role in the· locomotion of the animal and obtaining food is the major function of water Vascular system. 
  • The water vascular system of starfish consists of 
             1. madreporite, 
             2. stone canal, 
             3. ring canal, 
             4. radial canal, 
             5. Tiedemann’s bodies, 
             6. polian vesicles, 
             7. lateral canals and  
             8. tube feet.

1. Madreporite

  • The water vascular system of star fish starts from the madreporite, which is rounded and hard due to calcareous plate on the aboral surface of the central disc of the body. 
Figure 1.

  • Its surface bears numerous fines radiating grooves or furrows, having at their bottom minute ciliated pores. 


  • Each furrow contains as many as 200 to 250 pores, which lead into very short and fine tubes called the pore canals as shown in Figure 1 above.
  • Each pore canal unite to form larger collecting canal called ampulla of stone canal as shown in Figure 1 above.
2. Stone Canal: 

  • Stone canal is a 'S' shaped tube opening on the oral side into a ring canal around the mouth. 
  • Its wall is supported by series calcareous rings hence called 'stone canal. 
Figure 3.
  • The lumen of the stone canal is lined by ciliated cells which draw the water current into canal.
  • The wall of the stone canal projects into its cavity like ridge that bifurcates into lamellae. 
  • Stone canal along with an axial organ is enclosed in a coelomic sac called axial sinus. 
  • The stone canal, axial organ and axial sinus these three together form the axial complex as shown in figure 4.
Figure 4.

3. Ring Canal: 

  • It is wide, slightly pentagonal ring which forming round the oesophagus. 
  • Angles of pentagon lies in the radial canal.
  • From outer surface of canal it gives off 5 radial canals entering in each arm.
  • The radial canal runs up to the tip of each arm.
Figure 5.

4. Radial Canal

  • The radial canals carry water from ring  canal and distribute to Ampullae; which have a tube feet theough which the water moves. 
Figure 6.


5. Tiedemann's Bodies: 

  • These are also known as racemose gland. They are of 5 pairs.
  • On the inner side of ring canal its gives off small irregularly shaped bodies which are known as the tiedemann's bodies.  
  • There are 9 Tiedemann's bodies 1 is absent from where stone canal arises as shown in figure 7. below.
  • 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.
Figure 7.

6. Polian Vesicles: 
Figure 8.
  • Polian vesicles are large, thin walled, pear shaped sac.
  • In each inter radius of the ring canal it gives off  2 to 4 Polian vesicles. 
  • They act as contractile structures which mainly store s water. 
  • The main function of these vesicles are found to regulate the pressure in water vascular system. 
  • These vesicles also helps in manufacture amoeboid cells.

7. Lateral Canals
  • Each radial canal, arises two series of narrow lateral canals in each arm, along its entire length.
  • Each lateral canal opens into a tube foot, the opening is guarded by a valve which prevent back flow of fluid into radial canal.


Figure 9.
8. Tube Feet: 

  • The tube feet are arranged in grooves along the arms.
  • They operate through hydraulic pressure. 
  • They are used to pass food to the oral mouth at the center, and can attach to surfaces.
  • Each tube foot can be distinguished into three regions, a rounded sac-like ampulla, a middle tubular podium and a cup like sucker at the lower end.



 Function:


The tube feet are locomotory and respiratory in function. 
They also help in attaching the body to the substratum and in capturing and handling the food.


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