Study of Water Vascular System of Starfish

Title:- Study of Water Vascular System of Starfish 

Water Vascular System:-

The water vascular system or ambulacral is a sort of hydraulic pressure mechanism and consists of a madreporite, stone canal, ring canal, radial canal, Tiedmann’s bodies, pollian vesicle, Lateral canal & tube feet. This system is concerned with locomotion.

1) Madreporite – A flat disc with radiating grooves at the bases of bivium It is a hard, rounded, Calcarious plate on the aboral surface. It leads to a stone canal.
2) Stone Canal – A ampulla, opens into a vertical ‘S’ shaped stone canal. It is a cylindrical tube. Supported by calcareous rings. The stone canal runs downward from the madreporite to join the ring canal. 
3) Ring Canal– It is a wide, five-sided, or pentagonal, ring like canal situated around the mouth. It lies just the inner side of the peristomal ring. 
4) Tiedmann’s Bodies – The ring canal gives off inter-radially a pair of small vesicles on its inner side called racemose gland or Tiedmann’s Bodies. These are small, yellowish rounded bodies. There are only nine Tiedmann’s bodies, the 10th being absent & its position taken by the stone canal. Tiedmann’s bodies manufacture the amoebocytes which are phagocytic in function.
5) Pollian vesicles – The ring canal gives off in each inter-radius a large, thin-walled pear-shaped Sac called Pollian vesicles. Their number is variable from 2 to 4. These are contractile structures with store water & supposed to regulate the pressure in the water vascular system & manufacture amoeboid cells.
6) Radical Canal – Ring Canal from its outer surface gives off five, long, ciliated radical canals into each arm. These canals run up to the tip of the arm. 
7) Lateral Canal – During the course of radial canals it gives off on either side a series of short, narrow, transverse branches, called lateral or Podial Canals. They are arranged alternately long and Short & open into tube feet.
8) Tube Feet – There are two alternating rows of tube feet on either side in the ambulacral groove of each arm. Each tube feet or podium is a hollow, elastic, thin-walled sac-like part is called Ampulla, a middle Podium & lower disc, like structure- Sucker.

        The ambulacral system (water vascular system) mainly helps in locomotion, and adherence to substratum & plays an important role in Respiration.

• Temporary Preparation of Gonads from Starfish:-

        Asterias is unisexual animal. The male gonads (testis) & female gonads (ovaries) have similar forms & structures but they differ in color. The testis are pale gray while the ovaries are pink to orange in the fresh state.

•Location – There are a pair of Gonads. Each pair is lie-free laterally in the base of each arm between the pyloric caeca & Ampullae.
•Structure – Each gonad is a branched structure Consisting of masses of small rounded follicles like bunches of grapes.

•Study of T.S of an arm & Types of Pedicellariae:-

•T.S. Passing through the arm of Starfish:-

1. The arm is covered by cuticle, ciliated epidermis & thick dermis. 
2. The dermis contains numerous perihaemal spaces and ossicles.
3. The epidermis and dermis show spines, Pedicellariae, and dermal branchiae.
4. In the T.S. the aboral surface appears thick and convex arch while the oral surface is like an inverted ‘U’ shape.
5. The arm encloses Coelom which contains a fair of pyloric Caeca, each suspended by two longitudinal mesenteries from the aboral surface.
6. On the oral surface, the ambulacral groove is Supported by two elongated ambulacral ossicles meeting at the summit of the groove.
7. Above the ambulacral groove runs a radial canal which is jointed on each side by a podial branch to two ampullae called lateral water Canals.
8. A radical hyponeural sinus is seen below the radial canal.

•Types of Pedicellariae:- The pedicellariae are modified spines that occur in space between spines in clumps around the bases of spines all over the body. They are microscopic pincer-like or jaw-like bodies.

• Structure of Pedicillariae:-

The stalked or pedunculate type of pedicellariae is found in the genus Asterias. Each Pedicellariae consists of a short, Flexible & fleshy stalk, but there is no internal calcareous Support. The stalk bears three calcareous plates or ossicles, a basilar Plate at its top & two jaws or valves. The jaws are articulated with basilar plates & serrated along their opposed edges. The pedicellariae having three calcareous pieces & stalk are called forcipulate pedicellariae. They are covered with epidermis which is richly supplied with sensory & gland cells.

•Types of pedicellariae:-  

          There are two types of forcipulate pedunculate Pedicellariae found in Asterias. These are forceps or straight types of scissors or Crossed types.

•Foreceps or Straight Type:-

        It is a simple type in which the two jaws are more or less straight & attached basically to the basal piece. When Pedicellariae is closed the jaws remain parallel & meet throughout their length like Foreceps. The jaw can be opened or closed by one pair of abductor muscles to open them.

•Functions of Pedicellariae:-

        The pedicellate performs different functions. They are useful for the Protection of delicate skin, gills, or papulae & keep the body surface free from debris & foreign organisms. They also serve as defensive & offensive organs.

•Study of larval forms in Echinodermoda:- (Bipinnaria Lava )

1. This is the free-living larval stage of Asteroidea.
2. Bilaterally symmetrical & somewhat angular in shape. 
3. The anterior end of the larva is enlarged to form a Pre-oral lobe. The ciliated border of the pre-oral lobe is Called the Pre-oral bond which encircles the mouth. The pre-oral bond separates completely from the rest of the longitudinal bond or post-oral bond.
4. The larva develops three lobes on either side of the body which are bordered by post-ciliary bond.
5. The larva is free-swimming.
6. The larva shows the mouth, esophagus, stomach, and intestine.
7. The bipinnaria larva changes into the next larval stage called branchiolaria larva.