External part of Body (oral & ab oral Surface) , Pedicellaria & water vascular system of star fish, & water vascular system of star fish

1. Shri Shankaracharya Mahavidyalaya, Junwani , Bhilai
Body Surface & water vascular system of Star fish
Dr. Sonia Bajaj
(Head of Department)

2. Introduction-
Star fish or Sea star is common echinoderm in the sea water.
• Its Zoological name is Asterias rubens.
• Star fish dwells on the bottom of the sea.
• It is a benthonic form.
• They are more common on hard rocky sea bottom, Star-fish is a carnivorous animal.
• It creeps slowly on the sea bottom.
• It can bend or twist in many ways.
• It has the power of autonomy (Self amputation).
Shape:
• The body, is compressed on oral-aboral axis.
• It shows a central disc. From this disc five arms will project.
• They are symmetrically arranged.
• The arms are board proximally and are free at the distal end.
• The arms occupy the radial axis.
•
Size: The smallest star fish is one cm in diameter, where as the largest one is 200 cm in
diameter.
The average size varies from 10 to 20 cm.
Colour: Star fish show brilliant colours. Yellow - brown or orange colours are common.

3. External Features: The body of Asterias is star shaped
and looks like a sea star.
Surface of the Body: The body shows two surfaces.
Oral and Aboral.
• The oral surface faces the bottom of the sea.
• The centre of the oral surface contains mouth.
• The aboral surface is directed upwards. It is slightly
convex.
• The oral and aboral surfaces are not dorsal and
ventral sides of the body, but right and left sides of a
bilaterally symmetrical animal.

4. Oral surface
1. Mouth: It is round opening. Situated in the centre of
pentagonal central disc and surrounded by mouth
papillae.
2. Ambulacral grooves: From the comers of the mouth
five ambulacral grooves will start and run along the
middle of the arms.
3. Tube feet or Podia: Each ambulacral groove
contains 4 rows of tube feet. They are soft and extensible
tubular processes. Each tube feet end- in a sucker. The
tube feet are useful for locomotion and food collection.
4. Ambulacral spines: Each ambulacral groove is
guarded on each side by 2 or 3 rows of spines. These are
movable. These spines are aggregated into five groups
called Mouth papillae.
5. Eye: The eye is small and bright red spot. It is present
at the end of each arm. It is light sensitive.
6. Tentacle: At the end of each arm a small non-
retractile tentacle is present. It is olfactory in function.

5. Aboral surface
1. Anus: It is a small opening. It is nearly in the middle of aboral
surface.
2. Madreporite: It is flat, almost circular plate. It is sieve plate
like structure. It leads into a stone - canal of water vascular
system. Madreporite is placed in an inter-radius of the central
disc. It converts the radial symmetry of the animal into bilateral
symmetry.
3. Spines: The spines of aboral surface are white in colour. They
are arranged in irregular radial rows. The spines are short, and
stout. They are developed from the calcareous plates called
ossicles.
4. Dermal branchia : These are small finger like processes. They
come but through dermal pores. Dermal pores are present in
between the ossicles. These papulae are also called gills. They
are respiratory in function.
5. Pedicellariae: Pedicellariae are scattered all over the body.
These are present in between the oral and aboral surface. On the
oral surface they are present attached to the bases of the spines.
Two type of pedicellariae occurs in starfish, first straight type
and second is crossed type of pedicellariae.

6. Structure: The pedicellariae are stalked. They are called
pedunculate type. Stalk is covered by epidermis which
has sensory and gland cells. It shows three calcareous
ossicles.
Basilar piece near stalk. Two jaws, the jaws are
articulate with the basilar piece. They can be opened or
closed like the jaws of a bird by muscles such
pedicellariae, are called forcipulate.
Kinds: Two types of forcipulate pedunculate
pedicellariae are seen in Asterias.
In the forceps or straight type-two basal ends of the
two jaws are arranged like Forceps.
In crossed or scissors type -the two basal ends of the
two jaws are crossed and look like scissors. The jaws are
also operated by three pairs of muscles.
Functions:
• They protect the delicate gills or papulae.
• They remove the debris form body.
• They are helpful in the capture of small prey.

7. WATER VASCULAR SYSTEM IN STARFISH
Introduction –
The water vascular system is enterocoelic in origin and arises from the left hydrocoel. It
exhibits radial symmetry from the beginning and is equally developed in all echinoderms.
This system lies just above the haemal system. It is primarily locomotory in function and
also sub-serves the function of tactile and respiratory organs in some cases. The excretory
role of water vascular system, suggested by some workers, is not yet fully ascertained.
Histological picture reveals that the canals have an inner lining of flat ciliated epithelium, a
layer of longitudinal muscles, a connective tissue layer and an outermost layer of flat ciliated
cells.
In Echinoderms a peculiar system is met with. It is filled with sea water, it is called
water vascular system or Ambulacral system. The entire system is lined with ciliated
epithelium. This system is well developed in Asteroidea. It contains Madreporite, stone
canal, ring canal, 5 radial canals, Tiedemann's bodies, lateral canals and tube feet.

8. Madreporite: A calcareous plate like
structure is present on the aboral surface of
the central disc of star fish. It is placed near
to two arms and these two arms are called
'Bivium.' On surface of the madreporite
grooves of furrows are present. Each
furrow contains a 200 number of pores.
Hence it is called sieve plate. These pores
led into small canal which open into a
stone canal open into a bag like ampulla.
Stone Canal: It is a 'S' shaped canal, it is
called Madreporic canal. It travels towards
the oral side on unite with ring canal at one
of inter radius. The walls of stone canal
are strengthened by calcareous rings.
The inner surface of stone canal is lined
with flagellated cells. The movement of
flagella will draw water currents into the
stone canal. The wall of the stone canal
shows a ridge on one side called
'Lamellated ridge.'

9. Ring Canal: It is penta - radial and is
present arround the mouth, on the oral
side. At each inner radius, it shows
pollan vesicles and Tiedemann's bodies.
Pollan Vesicle: In the Asteroidea groups,
four muscular like poiian vesicles are
present at the 4 inter radi. Some scientists
believe that they store water and are
considered as reservoirs. Some scientists
consider that they produce amoebocytes.
Tiedmann's Bodies: Usually in Asterias
five pairs Tiedeman's bodies are present.
On either side of the pollan vesicle two
Tiedemann bodies are present. At the
stone canal union with ring panal only one
Tiedmann body is present. They are
lymphoid sac like structures. They are
believed to produce amoeboytes.

10. Radial Canals: From the ring canal five
radial canals arise and run throughout the
entire length of the arm. Each radial canal lies
below the ambulacral groove of the oral
surface of the arm. Each radial canal ends at
the tip of the arm as a tentacle. It is olfactory
in function.
Lateral Canals: From the radial canal of each
arm pairs of lateral canals will arise and they
end with tube feet.
Tube Feet: The basal part of the tube feet is
bulged and is called ampulla. Each tube
foot is a hollow, elastic, thin walled close
cylinder bearing a sucker at its free end. It
continues as a long tube feet which ends
with a 'Sucker'. The ampulla contains
circular and longitudinal muscles. The long
tube feet like structure contain only
longitudinal muscles. Lateral canal will open
into ampulla and is guarded by a valve. In
some case the tube –feet also serve as a tactile
and respiratory organs.

11. Functions of Water vascular System: This mainly used for locomotion and food collection.
1) Locomotor function: The contraction of ampulla extends the tube feet. The tube feet will
emerge out of the arm and attaches to the substratum with the help of suckers. The water
from ampulla will never enter into lateral canal because of the presence of valves.
The longitudinal muscles of the tube feet will contract and the animal is pulled forward and
the Podia becomes short. The fluid is drawn back into the ampulla. Thus relaxation and
contraction of tube feet will bring locomotory movement in Star fish. Usually the
locomotion is carried on by tube feet of one or two arms in one direction only.
2) Food collection: Star fish utilises its tube feet. Then it feeds the soft material of
Molluscan animals.

12. References-
Modern text book – R.L.Kotpal
Jantu Vigyan- S.M. Sexsena
Jantu Vigyan- Dr.H.N. Baijal