2. Basic Features of the Water Vascular System Unique feature of the echinoderms. Unique feature of the echinoderms. Consists of canals and appendages of the body wall. Consists of canals and appendages of the body wall. This system is derived from the Coelom i.e. mesodermal in origin. This system is derived from the Coelom i.e. mesodermal in origin. The canals are lined with a ciliated epithelium and filled with fluid. The canals are lined with a ciliated epithelium and filled with fluid. It is also called as the ambulacral system. It is also called as the ambulacral system. Functions as a means of locomotion, food and waste transportation and respiration. Functions as a means of locomotion, food and waste transportation and respiration. Basic structure of the water vascular system is the same in all echinoderms, but varies slightly among the 6 classes of echinoderms. Basic structure of the water vascular system is the same in all echinoderms, but varies slightly among the 6 classes of echinoderms. Classes: Asteroidea, Ophiuroidea, Echinoidea, Holothuroidea, Crinoidea, Concentricycloidea Classes: Asteroidea, Ophiuroidea, Echinoidea, Holothuroidea, Crinoidea, Concentricycloidea

3. Class Asteroidea This class consists of sea stars or star fish. This class consists of sea stars or star fish. These are typically pentamerous, with most species possessing 5 arms. These are typically pentamerous, with most species possessing 5 arms. The sun stars however possess 7 to 40 arms. The sun stars however possess 7 to 40 arms. The mouth is located in the centre of the underside of the disc and arms and is called the oral surface. The mouth is located in the centre of the underside of the disc and arms and is called the oral surface. From the mouth, a wide furrow extends radially into each arm. From the mouth, a wide furrow extends radially into each arm. Each furrow, called the ambulacral groove, contains 2 or 4 rows of small tubular projections, called tube feet or podia. Each furrow, called the ambulacral groove, contains 2 or 4 rows of small tubular projections, called tube feet or podia. The aboral surface (upper) bears an inconspicuous anus in the centre of the disc and a large button like structure, the madreporite, towards one side of the disc between two of the arms. The aboral surface (upper) bears an inconspicuous anus in the centre of the disc and a large button like structure, the madreporite, towards one side of the disc between two of the arms.

4. Asteroid Water Vascular System Madreporite: On the aboral surface. Connects the internal canals of the water vascular system to the outside. Stone Canal: Connects the madreporite and the ring canal. Descends to the oral side from the aboral side. So called because of the calcareous deposits on its wall. From the ring canal arises the radial canals, extending to each arm. From each radial canal, arise, lateral canals, alternately. The inner side of the ring canal gives rise to 4 or 5 pairs of greatly folded pouches, the Tiedmann’s bodies (that produce certain coelomocytes). Attached inter- radially to the ring canal are polian vesicles.

5. Tube feet in Asteroids Each lateral canal is provided with a valve and terminates in a bulb (ampulla) and a tube foot. The ampulla is a small muscular sac bulging towards the aboral side of the perivisceral coelom. The ampulla opens into a tube/canal and opens into a tube foot or a podium. The tip of the podium is flattened, forming a sucker. The podia are arranged in two rows where the lateral canals are all of the same length, or in four rows, where, they are alternately long and short.

6. Functioning of the tube- feet The entire water vascular system is filled with a fluid that is similar to the sea water except that it contains coelomocytes, a little protein and high potassium ion content. This systems works as a hydraulic system and aids in locomotion. Ampulla contracts valve in lateral canal closes water forced into the podium, and podium elongates podium contacts the substratum and sucker adheres (adhesion and deadhesion are chemically mediated). After the adhesion of the sucker the muscles of the podium contract the podium shortens and the water is forced back into the ampulla. During movement, each podium performs a sort of stepping motion. The podium swings forward and grips the substratum and then moves backwards. The action of the podia is highly coordinated. The madreporite, stone canal, ring canal, the polian vesicles and the radial canal help in maintaining the proper volume of fluid for the proper functioning of the tube feet.

7. Class Ophiuroidea This class consists of brittle stars. This class consists of brittle stars. The extremely long arms of ophiuroids are more sharply set off from the central disc. The extremely long arms of ophiuroids are more sharply set off from the central disc. There is no ambulacral groove and podia play little role in locomotion. There is no ambulacral groove and podia play little role in locomotion. The basic organization of the water vascular system is similar, except for a few differences. The basic organization of the water vascular system is similar, except for a few differences. The paired lateral canals of ophiuroids contrast with the staggered arrangement in other echinoderms. The paired lateral canals of ophiuroids contrast with the staggered arrangement in other echinoderms. Ampullae are absent, probably correlated with the reduction of the arm coelom, but a valve is present between the podium and the lateral canals. Ampullae are absent, probably correlated with the reduction of the arm coelom, but a valve is present between the podium and the lateral canals.

8. Class Echinoidea Echinoids are the free moving echinoderms that include sea- urchins, sand dollars etc. Echinoids are the free moving echinoderms that include sea- urchins, sand dollars etc. Echinoidea, meaning like a hedgehog, refers to the movable spines that cover the bodies of most of these animals. Echinoidea, meaning like a hedgehog, refers to the movable spines that cover the bodies of most of these animals. The echinoid body does not have arms. They are oval/spherical or greatly flattened along the oral/aboral axis. Radially symmetrical adults. The echinoid body does not have arms. They are oval/spherical or greatly flattened along the oral/aboral axis. Radially symmetrical adults. Flattening and suturing together of the skeletal ossicles into a solid case (test). Flattening and suturing together of the skeletal ossicles into a solid case (test). The water vascular system is essentially like the sea stars. The water vascular system is essentially like the sea stars. The podia help in locomotion. The podia help in locomotion.

9. Class Holothuroidea Holothuroids are also known as sea cucumbers. Holothuroids are also known as sea cucumbers. The body of the holothuroid is not drawn into arms and the mouth and the anus are on the opposite poles. The body of the holothuroid is not drawn into arms and the mouth and the anus are on the opposite poles. The ambulacral areas are arranged meridionally around the polar axis. The ambulacral areas are arranged meridionally around the polar axis. The elongated cucumber shape of the body of the animal, forces the animal to lie with the side of the body against the substratum. The elongated cucumber shape of the body of the animal, forces the animal to lie with the side of the body against the substratum. Although the water vascular system is basically like the other echinoderms, but there are some differences. Although the water vascular system is basically like the other echinoderms, but there are some differences. The madreporite is not on the body surface and is unattached in the coelom. The madreporite is not on the body surface and is unattached in the coelom. Perivisceral coelomic fluid, rather than sea water, enters the system. Perivisceral coelomic fluid, rather than sea water, enters the system.

10. Class Crinoidea Crinoids are the most ancient and most primitive of the living classes of echinoderms. Crinoids are the most ancient and most primitive of the living classes of echinoderms. Attached, stalked crinoids, called sea lillies, flourished during the paleozoic era. Attached, stalked crinoids, called sea lillies, flourished during the paleozoic era. This class also includes, feather stars, which are free living. This class also includes, feather stars, which are free living. The basic structure of the water vascular system is similar to that of echinoderms. The basic structure of the water vascular system is similar to that of echinoderms. A single madreporite is absent. Instead, numerous (often hundreds) of separate surface pores and pore canals are present which open into the coelom near the stone canals. A single madreporite is absent. Instead, numerous (often hundreds) of separate surface pores and pore canals are present which open into the coelom near the stone canals. There are as many number of stone canals as well. There are as many number of stone canals as well. Ampullae are absent. Ampullae are absent. One lateral canal supplies a cluster of three podia. One lateral canal supplies a cluster of three podia. Hydraulic pressure for extension is generated by contraction of the radial water canal, which is provided with muscle fibres. Hydraulic pressure for extension is generated by contraction of the radial water canal, which is provided with muscle fibres.

11. Class Concentricycloidea These are the latest discovered class of echinoderms, disovered in 1983- 1984 near New Zealand. These are the latest discovered class of echinoderms, disovered in 1983- 1984 near New Zealand. These animals are generally 2- 9mm across and are covered aborally with plate like ossicles. These animals are generally 2- 9mm across and are covered aborally with plate like ossicles. Marginal spines are located around the periphery. Marginal spines are located around the periphery. The water vascular system is peculiar and apparently having two ring canals, with the podia arising from the outer canal. The water vascular system is peculiar and apparently having two ring canals, with the podia arising from the outer canal.