Question

Explain the water vascular system in Echinodermata. Include the terms: hydrocoel, madreporite, ring canal, polian vesicle, tiedemann’s body, radial canals, lateral canals, podia, duo gland. Written or drawn is okay.

Answer 1

Water vascular system is the most distinctive features of echinoderms . It is a modified part of coelom consisting canal system which are filled with water or watery fluid . This system acts like circulatory system of body maintaining continuous flow of water in and out of the body. The purpose of the system is locomotion ( it is most peculiar and interesting role of water vascular system . Echinoderm's body is moved by the stepping action of tube feet ),   capture and food transport ( food particle is captured by tube feet and then transported through canal system. ) , respiration ( tube feet also serve as equivalent of gills during respiration, the thin wall of tube feet helps in exchange of gases. They absorb oxygen and release carbon dioxide in water ) .   

Water vascular system of echinoderms consists of madreporite or sieve plate, stone canal, ring canal, radial canal, tube feet or podia.

1) madreporite - it is a perforated (with pores) plate like structure also known as sieve plate which allows the sea water to enter into the system i.e It works like a trap door .

2 ) stone canal- it starts from madreporite and opens into pentamerous ring canal . It transports water from madreporite to ring canal .

3) ring canal - it is main structural canal system receives water from stone canel and release water to radial canal .

Polian vesicle - certain echinoderm's ring canal contains at the outer side ( ring canal 's outer side ) bladder like small spongy structure known as polian sac . It apparently maintain the internal pressure in the water vascular system and also act as reserve suppliers of fluid .

Tiedmann's body- it is usually rounded glandular structure , and are usually two in each inter radius (inner side of ring cannal ) the function of it is to produce coelomic corpuscle which are released into ring canal and also it helps in filtration of the fluid .  

4) radial canal - it arises from each angle of ring canal and runs through the length (along ambulacral grooves)  of each arms . Transport water from ring canal to lateral canal.

5) lateral canal or podial canal  - it arises from radial canal and ends in tube feet. And it transport water from radial canal to tube feet. Lateral canal posses vulves which prevents back flow of water and control the water flow toward podia or tube feet

6) tube feet or podia - there are two double rows of tube feet in each arm. It is tube like hollow elastic appendages projected out - ward from lateral canal . Water exit the system through tube feet  

It has three distinguished part - a) a rounded sac like ampula it is mascular structure. b) in middle there is tubular podium c) and a cup like sucker at the lower end of podium . It helps to attach to the substratum

Duo gland - tube feet ( sucker part) contains adhesive organ named duo gland which consists of three types of cells . Adhesive gland cell produce protenacious glue like substance which helps to attach. De adhesive or releasing gland cell ​​​​​​, which provides de-adhesive protein which helps the echinoderms to release the substratum (for this dual purpose named duo gland ) anchor cell or supporter cell- which provides mechanical support during attachment or releasing substratum .

Water madreporite stone canal ring canal radial canal lateral canal podia - water exit the body