In this article we will discuss around Water Vascular system of Echinoderms:- 1. Introduction to Water Vascular system 2. Contents of Water Vascular mechanism 3. General setup 4. Modifications 5. Functions.

Introduction to Water Vascular System:

The water vascular system is enterocoelic in ori­gin and arises indigenous the left hydrocoel. The exhibits radial symmetry from the beginning and is equally arisen in every Echinoderms.

This device lies just above the haemal sys­tem. That is primarily locomotory in function and additionally sub-serves the function of tactile and also respiratory organs in some cases. The excre­tory duty of water vascular system, suggested by part workers, is no yet completely ascertained.

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Histological snapshot reveals that the ca­nals have an within lining of level ciliated epithelium, a class of longitudinal muscles, a connective organization layer and an outermost great of level ciliated cells.

Contents the Water Vascular System:

The canals the the water vascular mechanism contain a fluid of albuminous nature. That con­tains sea water and leucocytes. Visibility of red corpuscles is recorded in an Ophiuroid, Ophiactis virens. Binyon (1964) has shown that the level of potassium in the liquid may be as much as 60% over the sea water value. Boolootian (1966) has actually recognised 14 different species of amoebocytes in this fluid.

General setup of Water Vascular System:

The water vascular mechanism in various classes the Echinodermata has almost the very same structural organisation. That comprises that a few canals along with some appendages enclosed to these canals. The usual arrange­ment that the water vascular system is exhib­ited by Asterias.

The water vascular system contains a circumoral canal (circular ambulacral or ring canal) situated around the mouth which provides tubular radial extensions, referred to as radial canals. The number of the radial canals is normally five. Yet the number corre­sponds to the number of the radii of the body.


Each radial canal ends thoughtlessly at the finish of the arm and gives off along its course lateral vessels, each joining a tube-foot. Each tube- foot is a hole conical or cylindrical procedure with an ampulla and also a terminal sucker. The junction in between the lateral vessels and the tube-feet is listed with valves which aid in locomotion.

The contraction of the ampul­lae results in the expansion of the tube-feet. A short, slightly curved, cylindrical and also verti­cally disposed rock or sand canal is present in between the madreporite and also the ring canal. The rock canal opens into the ring canal at the dental end and also into the madreporic ampulla at the aboral end.

The madreporite is a skel­etal plate-like structure placed at the aboral side. The is perforated by pores, called the madreporic pores, which lead into madreporic ampulla or vesicle from whereby the stone canal starts. The rock canal is surrounded by a wider canal, referred to as axial sinus, the wall of which i do not care folded to kind the axial body organ or dorsal body organ or ovoid gland or heart. The duty of axial body organ is not completely known.

Besides the main vessels, some append­ages become linked with the system. Inter-radially located and connected v the ring canal, there room polian vesicles and also Tiedemann’s bodies. The Polian vesicles room bladder-like sacs through narrower neck.

They are contractile and usually manufac­ture amoeboid cells. The Tiedemann’s bod­ies are glandular in nature and also consist that a variety of branched tubules. They space yel­lowish in colour and give origin to cells for the water vascular system.

Modifications that the Water Vascular system in various Classes:

The water vascular system is equally occurred in every Echinoderms and also has basi­cally the very same structural plan. In the differ­ent classes, slight deviations indigenous the basic plan space encountered. The sports are as result of their adaptations to different modes that living.


In Asteroidea (Fig. 21.7B), the is a calcareous sieve-like plate and also is situ­ated aborally. The rise in variety of the madreporite is observed in plenty of Asteroidea. The number of madreporites is 3 in Asterias capensis, 4 in A, tenuispina, 16 in Acanthaster echinites. The madreporite is listed with many second water-pores. Most of the water-pores lead into stone canal and rest into the axial sinus in adults.


The water-pores are many in number and also develop indigenous one major larval water-pore. Favor Asteroidea, in Echinoidea (Fig. 21.16) additionally the madreporite possesses plenty of pores, yet Echinocyamus pusillus, is strange in having actually only one water-pore. In Ophiuroidea, the madreporite has actually one water-pore, but in Ophiurae and also Astrophytidae there space sev­eral water pores.


In Holothuroidea true madreporite is absent. An excellent variations space observed regard­ing the opening of the rock canal. In Pelagothuria it opens to the exterior through one pore and in countless Elasipodidae there room 2 come 50 or more pores. But in some Elasipodidae and also Molpadidae the rock canal opens right into the coelom by many pores instead of open­ing come the exterior.

In the rest of the Holothurians, the rock canal opens right into the axial sinus which in turn opens come the exte­rior through one or much more water-pores i m sorry are comparable to madreporite. The madreporite in this case may ideal be called as inner madreporite.

In Crinoidea, madreporite is represented by well water-pores ~ above the human body surface and these water-pores lead directly into the human body cavity. The water-pores are recorded to be 1500 in Antedon bifidia.

Stone canal:

Normally the stone canal is a short, contempt curved and vertically dis­posed cylindrical tube. The opens into the ring canal in ~ the dental end. That is enclosed by the wall of another wide canal, the axial sinus.

In Asteroidea, the stone canal is one and also ‘S’-shaped. But in Asterias rubens, there space two stone canals. The wall surface of the stone canal is detailed with calcareous ossicles. Devel­opment the a longitudinal ridge-like projec­tion provides the rock canal complicated in the different members that the Asteroidea (Fig. 21.37).


The following conditions are encoun­tered:

(1) In Echinaster purpureus, the fold tasks as a ridge into the canal. This repre­sents the easiest condition.

(2) In Asterina gibbosa, the cost-free terminal end divides into two lamellae which might be coiled. This is watched in Asterias and Gymnasterias.

(3) In Astropecten, the coiled lamellae come to be very complicated and extend between the wall surfaces from one side to another of the lumen.

(4) In Culcita and also Astropecten aurantiacus, the whole lumen becomes separated into a variety of irregular chambers.

In Echinoidea, the rock canal is just one and has soft membranous wall devoid of calcareous matter. In Cedaris, the wall surface of the stone canal is detailed with calcareous deposit. The stone canal has actually an ampulla below the madreporite.

In Ophiuroidea, the stone canal is devoid of calcareous deposition and opens in one of the dental plates (Sedjwick, 1898). In Trichaster elegans, there room five rock canals. In Ophiactis virens, the stone canals are many.

In Holothuroidea, the rock canal is mostly solitary but in some cases it might be an ext than one. The number of accessory stone canal is likewise variable. Its wall surfaces are detailed with calcareous matters.

The open­ing the the stone canal shows biggest varia­tion, specifically in Holothurians. The stone canals in every Holothurians are attached to human body wall. In Pelagothuria, the stone canal opens to the exterior by one or plenty of pores. This also is true in many Elasipodidae.

In her one, the rock canal is branched. In some Elasipodidae and Molpadidae the stone ca­nal end blindly and also opens internally right into the coelom by numerous pores together in the genus Elasipoda.

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In Crinoidea, stone canal therefore is ab­sent. Many tubes, there is no calcareous shop in your walls, arising from the ring vessel space the to represent of the rock canals of other groups.

Axial sinus and axial organ:

The axial sinus is variously emerged in different Echinoderms. The is quite distinct from the perivisceral cavity in adult excepting part Holothurians and Crinoids. The axial sinus is inconspicuous in Asteroids, very small in Echinoids and Ophiuroids. The axial organ, a wrinkles from the wall of the axial sinus, is present in all Echinoderms excepting Holothurians.

The axial organ comprises connective tissue and cells of germinal rudi­ment. In Echinoids the axial sinus end blindly and communicates v the stone canal. In Crinoids, the part of the coelom, right into which the tubes native the ring ship open, to represent the axial sinus. The axial body organ occupies the axis of the body. It con­sists the anastomosing canals installed in connective tissue.

Ring canal and Radial canals. The ring canal is a continuous structure in every Echinoderms and also is positioned round the mouth. It offers tubular prolongations follow me the radii, referred to as radial canals or radial ves­sels. In Asteroidea, the ring canal is pen­tagonal and also is situated in the buccal mem­brane (peristome). The is communicated with the exterior with the rock canal and also axial sinus.

In Echinoidea, the ring canal is situ­ated at the upper finish of the jaws and also gives 5 radial vessels. In Ophiuroidea, the con­dition is exact same as in Asteroidea. In Holothuroidea, the ring canal is situated about the oesophagus and the five raidal vessels expand towards the dental end and also again continue aborally follow me the radii of the body.

The radial vessels end blindly and also the terminal tentacle, characteristic of Asteroidea and Echinoidea, is absent. The number of radial vessels space five. They are lacking in Synaptidae. In situation of Crinoidea, the termi­nal tentacles are lacking and the radial vessels end blindly.

Lateral vessels and Tube-feet:

The radial vessels provide lateral vessels to the tube-feet. The tube-feet room cylindrical processes and also their cavities are constant with the water vascular system. The tube-feet own am­pullae at your inner ends and also suckers at the terminal ends. The ampullae are existing in every echinoderms, except Ophiuroidea and also Crinoidea.

In Crinoidea, terminal suckers are lacking and the tube-feet space sensory and respiratory in function. In plenty of Astropectinidae, every tube-foot is detailed with 2 ampullae. In all the members that the Asteroidea the tube-feet are listed with well-developed suctorial disc-like expan­sions.

In Echinoidea, the tube-feet present varia­tions. In Endocyclica, the terminal end of the tube-feet room suctorial and also supported by calcareous rings. In Cidaridae and Echinothuridae, little oral tube-feet task from the perforations that the ambulacral bowl which are olfactory in nature. In Clypeasteroids, the tube-feet are large and the walls room devoid that calcareous bodies. They aid in respiration.

The cylindrical tube- feet which room suctorial and listed with calcareous rings, are locomotory in function. However in Spatangoids, the tube-feet vary quite considerably which are because of their functional activities.

The tube-feet without suckers room respiratory in function; through suckers and calcareous ring space locomotory in function; with broadened terminal disc and also filaments around the mouth together the tactile organ; ro­sette feet act together prehensile organs and also seize food native the surroundings.

In Ophiuroidea, the orientation the the lateral vessels and the tube-feet is same as in Asteroidea, however they are devoid of ampullae and also are specifically sensory in function.

In Holothuroidea, lateral branches native the radial vessels go into the tube-feet and into the tentacles. Some lateral branches likewise emerge native the radial vessels and end blindly in the body wall. Ampullae are existing in the tube-feet and in the tentacular canals. The tentacular canals room devoid that ampullae in Elasipodidae where they arise straight from the ring canal.

Among the Crinoidea, in Antedon, every lateral branch indigenous the radial vessel provides three tube-feet. The tube-feet have ampullae. They are purely respiratory and sensory in function.

Polian Vesicle and Tiedemann’s Bodies:

The ring canal own bladder-like polian vesicles and gland-like Tiedemann’s bodies. In Asteroidea, the variety of polian vesicles varies greatly. Castle are completely ab­sent in Asterias rubens and A. Glacialis. Over there are instances where 2 or plenty of polian vesicles may be existing in each inter-radius as watched in Astropecten.

In this case, a few vesicles open into the ring canal by one common stalk (Fig. 21.38). The Tiedemann’s bodies space attached come the ring canal and are usually 2 in each inter-radius excepting the con­taining the madreporite where just one is present.


Amongst Echinoidea, in many Endocylica, a small spongy outgrowth in every inter-radius is present which is sup­posed to it is in the polian vesicle. Over there are 5 Tiedemann’s bodies in Echinoidea. In Ophiuroidea, in each inter-radius excepting that of stone canal, over there is a polian vesicle.

In Ophiactis virens, besides two or 3 polian vesicles opened in each inter-radius, over there are countless tubular canal that Simroth (sup­posed to be respiratory in function). The Tiedmann’s bodies show up to be wanting. Part authorities to express some structures ho­mologous v Tiedmann’s bodies.

Some say that the radiant protrusions are discovered in some places. Hyman (1955) additionally refers the these space Tiedmann’s bodies. Fedetov (1926) has actually reported that the radial protrusion is associated with water ring in Ophiactum sericeum.

In Gorgonocephalus, a bunch that pouch-­like frameworks or branching tubules are present in water ring. The did not cite it together Tiedmann’s bodies however represented it together spe­cialized structure.

Hyman (1955) said probably this structure stated in these above ani­mals as homologous v the Tiedmann’s bodies. In Holothuroidea, usually one large polian vesicle is present. In some impressive cases more than one polian vesicle may be present. In Crinoidea, the polian vesicle and also Tiedemann’s bodies room absent.

Functions the the Water Vascular System:

1. Locomotion:

The main role of the water vascular device is to aid in locomotion. Echinoderms having suctorial podia (tube-feet) deserve to adhere to the substratum temporarily. The mecha­nism the locomotion has disputed in detail under the water vascular device of Asterias and also Echinus.

2. Respiratory and sensory:

In Ophiuroidea and also Holothuridea the tube-feet (podia) are primarily sensory in function. In Echinoidea (in consistent urchins), the tube-feet the the aboral side absence terminal disc and also are sensory in function (Hyman, 1955).

In spatangoids, the petaloids that the abo­ral surface are noted with lobulated po­dia without suckers and are thought to part respiratory in role (Loven, 1883).

3. Excretory:

Nitrogenous wastes are removed through the thin locations of the body surface such together the wall surfaces of tube-feet.