Water Vascular System In Echinodermata, Lecture notes of Animal Biology

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Water Vascular System

In

Echinodermata

By Dr. Purnima Das Bora Associate Professor Dhing Collage Note - 2

Introduction :-

Essential Parts of the Water Vascular System :-

The essential parts of the Water Vascular System are :-  The Madreporite  Stone Canal  Ring Canal  Radial Canals  Tiedmann’s bodies  Polian Vesticles  Lateral Canals  Tube feet

Fig.1 : Madreporite

 Stone Canal : It is an S – shaped canal. The walls are strengthened by a series of calcareous rings and hence the name. Internally the stone canal is lined with cilia , the movement of which draws the sea water from outside into the canal. One end of the tube opens to the outside through the madreporite. The other ends opens into a ring canal. The lumen of the stone canal is occupied by a ridge with spirally coiled lamellae.

 Ring Canal : It is a white pentagonal ring - vessel lying around the mouth.  Radial Canals : From its outer surface the ring canal gives off five radial canals , one entering each arm. The radial canal runs upto the tip of the arm and ends in the terminal tentacles.

 Tiedmann’s Bodies : The ring canal gives off inter radially from its inner surface 10 small yellowish rounded glandular bodies called Tiedmann’s bodies. In Asterias only 9 Tiedmann’s bodies occur , the position of the 10 th being occupied by the stone canal. They produce phagocytes.

 Lateral Canals : Each radial canal gives off many paired lateral canals on both the sides , which lead to a tube foot or podium. Each canal is provided with a valve to prevent backward flow of fluid into the radial canal.

 Tube Feet : The tube – foot is a hollow elastic thin walked closed cylinder. It consists of an upper sac – like ampulla , a middle tubular podium and a terminal disc – like sucker. Muscle fibres are present in the walls of the ampulla and the podium. The tube feet are capable of greater extension and when extended they come out through the ambulacral grooves.

Functions of the water vascular system :-

 The Water Vascular system has three main functions. They are as follows : 1/ Locomotion 2/ Food Capture 3/ Attachment 1/ Locomotion :

1. Starfish exhibits creeping movement with the help of tube feet at a speed of 15 cm/min
2. The water vascular system sets up a hydraulic pressure mechanism which brings about the locomotion.

8. The podia now contract. This causes the flow of water from the podia into the ampulla.
9. This results in the shortening of tube feet.
10. The suckers are released and the tube feet are raised and moved forward to repeat the process.
11. Food capture : The tube – feet are used to capture the prey. The suckers are used to open the shells of molluscs.
12. Attachment : The star fish can be attached to the rocks by the tube feet.

Recommended Books :-

 A TEXT BOOK OF INVERTEBRATES

BY NAIR , et at al ; SARAS PUBLICATION , 2014 . Page no :- 620 - 621. A TEXT BOOK OF ANIMAL DIVERSITY BY R.L KOTPAL ; RASTOGI PUBLICATIONS , 2020 Page no :- 391 – 403.