1. Illutsrated by:

2. Introduction
The echinoderms are exclusively marine
enterocoelous coelomata, triploblastic animals having
pentamerous radial symmetry derived from a original bilateral
symmetry without definite head or brain with an endoskeleton
of calcareous plates or spicules embedded in the skin with a
peculiar water vascular system of coelomic origin, pushing
out of the body surface, numerous small delicate projections
the podia or tube feet, with an ectodermal nervous system
without nephridia and with gonads opening directly to the
interior by special ducts.
The name “Echinodermata” literally means “spines or
prickly skinned” and refers to the conspicuous spines
possessed by their skin. This name was at first used by
“Jacob Klein” for echinods.
The Greeks applied the name echinas to the
hedgehog as well as the sea urchin; both having a prickly
appearance. It was “Leukart” who first established

3. General Characteristics
- The echinoderms are exclusively marine and are
among the most common and widely distributed of
marine animals.
- They occur in all seas from the intertidal zone to the
great depths.
- Radially symmetrical and nearly always
pentamerous.
- Body is triploblastic, coelomate with distinct oral and
aboral surfaces and without definite head and
segmentation.
- They are moderate to considerable size but none
are microscopic.
- Body shape rounded to cylindrical or star-like with

4. - Surface of the body is rarely smooth, typically it is
covered by five symmetrically space radiating grooves
called ambulacra with five alternating inter-radii or
inter ambulacra.
- Body wall consists of an outer epidermis, a middle
dermis and an inner lining of peritoneum.
- Endoskeleton consists of closely fitted plates
forming a shell usually called theca or test or may be
composed of separate small ossicles.
- Presence of water vascular or ambulacral system is
the most characteristic feature. It consists of tubes
filled with a watery fluid.

5. - Alimentary tract is usually coiled tube extending
from the mouth located on the oral surface to the
annus on the oral or aboral surface.
- Circulatory or haemal or blood lacunar system is
typically present.
- Excretory system is wanting.
- Nervous system is primitive, consisting of networks
concentrated into the radial ganglionated nerve cords.
- Sense organs are poorly developed.
- Sexes are usually separated (dioecious) with few
exceptions. Gonads are simple with or without simple
ducts.

6. - Reproduction is usually sexual; few reproduce
asexually or by regeneration.
- Fertilization is external, while few echinoderms
are viviparous.
- Development is indeterminate including
characteristic larvae which undergo
metamorphosis into the radially symmetrical
adults.

7. - Radially symmetrical and nearly always pentamerous.
- Body is triploblastic, coelomate with distinct oral and
aboral surfaces and without definite head and
segmentation.
- Surface of the body is rarely smooth, typically it is
covered by five symmetrically space radiating grooves
called ambulacra with five alternating inter-radii or inter
ambulacra.
- Endoskeleton consists of closely fitted plates forming a
shell usually called theca or test or may be composed of
separate small ossicles.
- Presence of water vascular or ambulacral system is the
most characteristic feature. It consists of tubes filled with a
Identifying Characters of Echinodermata

8. - Alimentary tract is usually coiled tube
extending from the mouth located on the oral
surface to the annus on the oral or aboral surface.
- Excretory system is wanting.
- Nervous system is primitive, consisting of
networks concentrated into the radial
ganglionated nerve cords.
- Sense organs are poorly developed.
- Sexes are usually separated (dioecious) with
few exceptions. Gonads are simple with or without
simple ducts.

12. Classsification: Classification of Echinodermata is not universally
taken yet. But at present, two format of classification can be seen.
One of them is given by G.Ulbaughs (1967). This format is
based on the basis of external features of living and extinct species.
Other one is given by A.B. Smith (1984). In this format,
Phylum Echinodermata is divided into two sub-phylum. Now we’ll
discuss about this classification________
Sub-phylum: Eleutherozoa

13. Class:Asteroidea
Characteristics:
- Starfishes or sea stars.
- Arms five or more and not sharply marked off from the
central disc.
- Tube feet in orally placed ambulacral grooves; with
suckers.
- Annus and madreporite aboral.
- Pedicellariae present.
- Free-living, slow creeping, predaceous and
scavengerous.

14. Characteristics:
Fossil Pelazoic Sea stars.
Platasterias latiradiata is
the only living species.
Class: Asteroidea

15. Characteristics:
They are living sea
stars.
Class: Asteroidea

16. Characteristics:
- Brittle stars and allies.
- Body star like with arms sharply marked off from the
central disc.
- Pedicellariae absent.
- Stomach sac like; no annus.
- Ambulacral grooves absent or covered by ossicles;
tube feet without suckers.
- Madreporite oral.
Example: Ophiura, Gorgonocephalus, Asteronyx.
Class: Ophiuroidea

17. Class: Echinoidea
Sub-Class: Bothriocidaroida
Sub-Class: Regularia
Sub-Class: Irregularia

18. Characteristics:
- A single row of plates in
each inter ambulacral
area.
- Without typical lantern.
- Madreporite radial.
Example: Single extinct
Ordovician genus
Bothriocidaris.
Class: Echinoidea
Sub-Class: Bothriocidaroida
Sub-Class: Regularia
Sub-Class: Irregularia

19. Characteristics:
- Body globular pentamerous,
with two rows of inter-
ambulacral plates in existing
members.
- Mouth central.
- Aristotle’s lantern well
developed.
- Annus central on aboral
surface with well developed
apical plates.
- Madreporite oral.
Example:
Palaeodiscus,Melonechinus,
Class: Echinoidea
Sub-Class: Regularia
Sub-Class: Bothriocidaroida
Sub-Class: Irregularia

20. Characteristics:
- Body oval or circular, flattened
oral-aborally.
- Mouth oral or displaced
anteriorly on oral surface.
- Annus marginal, outside the
apical system of plates.
- Tube feet generally not
locomotor.
Example:
Echinoneus,Cassidulus,Echinoc
yamus, Spatangus.
Class: Echinoidea
Sub-Class: Irregularia
Sub-Class: Bothriocidaroida
Sub-Class: Regularia

21. Characteristics:
- Sea cucumbers.
- No arms and no spines.
- Body elongate on oral-aboral axis, body wall
leathery.
- Mouth anterior surrounded by tentacles.
- Ambulacral grooves concealed; tube feet with
suckers.
- Usually with respiratory tree for respiration.
Example: Cucumaria, Holothuria, Molpadia,
Class: Holothuroidea

22. Sub-Phylum: Pelmatozoa
Greek word “pelmatos”
means stalk and Greek word
“zoois” means animal. That’s
mean Pelmatozoa stands for
“stalked animal”. Their
characteristics are stalked
and sedentary.
Class:Crinoidea
Characteristics:
- Sea lilies.
- Body attached during part or whole of life by an aboral
stalk.
- Mouth and annus on oral surface.
- Arms with pinnules.
- Tube feet without suckers; no madreporite, spines and
pedicellariae.
- Ciliated ambulacral grooves on oral surface.

23. General Morphology of Star Fish or Sea Star
There are too many varieties of species consist
in phylum Echinodermata. Among them Class
Anthozoa is rich of species. Metridium
marginatum, known as sea-star or star fish under
this class, here’s some description about this.
Classification:
Phylum: Echinodermata
Sub-phylum: Eleutherozoa
Class: Asteroidea
Order: Euasteroidea
Family: Forcipulata
Genus: Asterius
Species: Asterius

24. Shape :
The echinoderms present at a great diversity of organization.
The original biradial symmetry is often obscured by a well developed
radial symmetry. The most striking characteristic of the group is their
pentamerous radial symmetry, i.e. body can be divided into five parts
arranged around a central axis. The radially arranged parts are
called antimeres, with the mouth at centre.
Star fishes have a flattened body which is pentagonal or
produced into five, six or even more tapering arms. Bristle stars have
a small rounded central disc with five distinct, slender, jointed and
flexible arms. Sea urchins are hemispherical while sand dollars are
disc like with a cup like central disc bearing five branched arms.
Size:
Some fossil and dollars measure only 6mm in diameter, whereas a
fossil crinoid had a stem about 22 meters long. However, the living
echinoderms are of moderate size. The largest star fish, Pycnopodia
helianthoides is about 30 cm. across. The shell of the largest urchins
Echinosome hoplacantha has a diameter of 30 cm. One sea cucumber,
Synapta maculata, measures about 2 meters in length and 5cm in diameter.

25. Coloration:
Echinoderms adapted various types of color, such
as yellow, orange, brown & purple. The body has two
surfaces. The upper convex & darker side is called the
aboral & abactinal surface. The lower surface is flat, less
pigmented & is called the oral actinal surface.

26. Habit & Habitat:
Asterias are exclusively marine, bottom dwelling or
benthic animal, inhabiting various types of bottom mainly in the
littoral zone where they crawl about or may remain quiescent at
times. Asterias forbesi is found equally on hard, rocky, sandy or
soft bottom, while other species of Asterias are generally
solitary but under certain ecological conditions. Such as to
avoid direct sunlight or excessive drying, many individuals may
gather at some place for the purpose of protection. Most of
them are nocturnal, remain quiet in day time and become
active during night. They move by crawling on the bottom
mostly at a rather slow rate. All sea stars are carnivorous and
feed voraciously and almost any available slow moving or
sessile animals, chiefly on polychaetes, crustaceans, mollusks,
and other echinoderms. Many species of Asterias exhibits
various types of biological relationships such as parasitism and
commensalism etc. Sea stars have remarkable power of
autonomy and regeneration.

27. Food & Feeding
Mechanism:
Sea star is a
voracious carnivore. It
prefers to prey on
sedentary marine
animals like clams,
oysters, mussels,
snails, crabs,
barnacles, worms, and
even sea urchins and
other smaller star fish.
At times it also feeds
on small fishes and
injured and dead

28. Sea star ingests and digests food in a
fascinating manner. Prey is captured and held in
position by the arms and tube feet. It may be
interesting to note how a sea star devours clams and
other bivalves. It conveniently creeps over the clam,
arches its body over it and firmly attaches its tube feet
to two shell valves in such a way that the ventral
margin of the clam comes to lie in front of its mouth. It
then tries to pull apart the two valves held tightly
together by the powerful adductor muscles. A few
tube feet at the tips of arms are also attached to the
substratum to aid in the process. Pull is steadily
maintained till the adductor muscles of clam are
exhausted and give way. Adductor muscles cannot, as
a rule, remain in a continuous state of contraction for
long time. When the valves finally gape, cardiac
stomach of sea star is everted into the mantle cavity

29. Body Structure:
Oral Surface:
The side of the body, which in natural condition remains towards
the substratum and contain the mouth or oral opening is called oral
or actinal surface. The oral surface bears the following structures.

30. (i) Mouth:
On the oral surface, in the centre of the
pentagonal central disc is an aperture, the actinosome or
mouth. It is a pentagonal aperture with five angles, each
directed towards an arm. The mouth is surrounded by a soft
and delicate membrane. The peristomial membrane or
peristome and is guarded by five groups of oral spines or
mouth papillae.
(ii) Ambulacral Grooves:
From each angle of the mouth radiates a
narrow groove called the ambulacral groove which runs all
along the middle of oral surface of each arm.
(iii) Tube Feet or Podia:
Each ambulacral groove contains four rows of
locomotory organs, food capturing, respiratory and sensory
organs called tube feet or podia. The tube feet are soft.
Thin walled, tubular, retractile structures provided with
terminal discs or suckers.

31. (iv) Ambulacral Spine:
Each ambulacral grooves is bordered and
guarded laterally by two or three rows of movable
calcareous ambulacral spines which are capable of
closing over the groove.
(v) Sense Organs:
Sense organs include five unpaired
terminal tentacles and five unpaired eye spots. The lip
of each arm bears a small median, non retractile and
hollow projection. The terminal tentacles act as a
tactile and olfactory organ. At the base of each
tentacle occurs a bright red photo-sensitive eye spot
made up of several ocelli.

32. Aboral Surface:
The side of the body, which remains directed upward or
lowers the upper surface is convex & of light orange to purplish
color is called aboral or abactinal surface. The aboral surface
bears following structures________

33. (i) Annus:
A minute circular aperture, called the annus. It
is situated close to the centre of the central disc of aboral
surface.
(ii) Madreporite:
At the aboral surface of the central disc occurs
a flat sub-circular, asymmetrical & grooved plate called
madreporiteplate. Madreporite between the basis of two of
the five arms. The surface of the madreporite is marked by
a number of radiating, narrow, straight or slightly wavy
grooves with pores in them.
(iii) Spines:
The entire aboaral surface is covered with
numerous short, blunt, calcareous spines or tubercles. The
spines are variable in size and arranged in irregular rows
running paralleled to the long axes of the arms.

34. (iv) Papulae or Gills:
Between the ossicles of integument are
present a large number ofminute dermal pores.
Through each dermal pore projects out a very small,
delicate, tubular conical finger like, thin walled,
membranous & retractile projection called the dermal
branchia or gill or papillae.
(v) Pedicellariae:
Besides the spines & gills, entire aboral
surface is covered by manywhitish modified spines
like tiny pincers or jaws called pedicellariae. The oral
surface also bears pedicellariae. Each pedicellariae
consists of a long or short, flexible stalk having no
internal calcareous support.

35. Water Vascular System
The water vascular
system is a modified part of
coelom & it consists of a
system of sea water filled
canals having certain
corpuscles. It plays most vital
role in the locomotion of the
animal.
It comprises________
(i) Madreporite
(ii) Stone Canal
(iii) Ring Canal
(iv) Tiedemann’s Bodies
(v) Polian vesicles
(vi) Radial Canal
(vii) Tube feet

36. Here’s some description____________
(a) Madreporite:
The madreporite is rounded calcareous plates
occurring on the aboral surface of the central disc in inter radial
position. Its surface bears a number of radiating, narrow,
straight or wavy minute pores at its bottom.
(b) Stone Canal:
The ampulla opens into an s-shaped stone canal.
The stone canal extends downwards & opens into a ring canal,
around the more the walls of stone canal is supported by a
series of calcareous ring.
(c) Ring Canal:
The ring canal or water ring is located to the inner
of the peristomial ring of ossicles and directly above to the
hyponeural ring sinus. It is wide & pentagonal or five sided.

37. (d) Tiedemann’s Bodies:
The ring canal gives out inter-radially nine, small,
yellowish, irregular or rounded glandular bodies called
racemose or tiedemann’s bodies from its inner margins. The
tiedemann’s bodies rest upon the peristomial ring of ossicles.
(e) Polian vesicles:
The ring canal gives off on its inner side in the inter radial
position one, two or four little, pear-shaped, thin walled,
contractile bladders or reservoirs with long necks called polian
vesicles.
(f) Radial Canal:
Along each radius, the ring canal gives out a
radial canal which extends up to the tip of the corresponding
arm. Radial canal ics below the ambulacral ossicles and
terminates as lumen of the terminal tentacle.

38. (g) Lateral Canal:
In each arm, the radial canal gives out two
series of short, narrow, transverse branches called
lateral or podial canals. Each lateral canal is attached
to the base of tube feet & is provided with a valve to
prevent backward flow of fluid into the radian canal.
(h) Tube feet:
There are four rows of tube feet in each
ambulacral groove. A tube feet or podium is a hollow,
elastic, thin walled, closed cylinder or sac-like
structure having an upper sac-like ampulla, a middle
tubular podium & a lower disc like sucker.

39. Locomotion of Echinoderms:
Locomotion is performed with the help of water-vascular
system which sets up a hydraulic pressure. By the action of cilia
lining the ambulacral canals, sea water enters through madreporite
and fills up all canals of the system including the tube feet. Body is
moved by the stepping action of tube feet which are alternately
adhered to and released from the substratum. One or two arms, in
the desired direction of movement, are raised from the substratum.
Simultaneously the ampullae of tube feet to these arms contract by
the action of their circular muscles. This increases the hydraulic
pressure within the tube feet, which consequently elongate, extend
forward and adhere firmly to the substratum by vacuum action of
their suckers. Adhesion is further strengthening by mucus secreted
by the tips of the tube feet. Then, by muscular activity, tube feet
assume a vertical posture, dragging the body forward. Tube feet
then shorten by contracting their longitudinal muscles and forcing
some water back into their ampullae. Consequently, the suckers
release their hold on the substratum.

40. During locomotion, one or two arms serve as leading
arms, and all the tube feet extend in the same
direction in a coordinated manner. However, the tube
feet may not work in unison. As a result, the star
moves forward steadily but slowly, at a speed of
about 15 cm per minute. Sea stars can also climb up
the rock by the combined action of their tube feet.
I f a sea star is accidentally turned upside
down; it can correct its posture by folding or arching
its arms. In folding action, tips of one or two arms
twist to bring their tube feet in contact with the
substratum, thus permitting the whole body to fold
over and right itself. In arching the upturned body is
first raised on its arm tips and then rolled over.

41. Larval Development:
Development of a sea star includes three larval stages __
dipleurula, bipinnaria and branchiolaria.
(1) Dipleurula larva or early bipinnaria:
First larval stage in all echinoderms is called early
bipinnaria. This larva closely resembles a hypothetical dipleurula
larva. It is believed that all modern echinoderms have been
derived from a dipleurula-like ancestor. Early bipinnaria is an
egg-shaped and bilaterally symmetrical organism. An anterior
mid-ventral ectodermal invagination, called stomodaeum,
becomes continuous with the archenteron to form the larval
mouth. Blastopore becomes the larval annus. Archenteron
differentiates into a digestive tract made of oesophagus, stomach
and intestine. Uniform ciliation of gastrula is replaced in
dipleurula by two ciliary bands__ a perioral band surrounding the
mouth. Larva feeds actively on unicellular algae, particularly
diatoms. Food particles are collected from the water current
produced by the aboral or stomodaeal cilia. As larva swims
forward, with the help of perioral band of cilia, It rotates

42. (2) Bipinnaria larva:
Dipleurula soon forms on its front side a large preoral
lobe, which becomes bordered by a preoral loop of cilia.
Simultaneously, on each lateral side, it forms three lateral lobes
which become bordered by a postoral loop of cilia. Pre and
post-oral loops arise by the sliting of the perioral band of cilia.
Larva thus formed is called bipinnaria. It is bilaterally
symmetrical. It swims and feed freely and after some weeks
transforms into the next larval stage, the branchiolaria larva.
(3) Brachiolaria larva:
The lobes of the bipinnaria develop into long, slender,
ciliated, contractile structures called larval arms. From the
preoral lobes arise three, short and non-ciliated appendages,
each ending in a sucker or adhesive disc. The appendages are
called bipinnarian arms or fixing processes. Larva is now called
bipinnaria. It is also bilaterally symmetrical and swims and
feeds actively. It gradually metamorphoses into a small sea star.

43. Larval Forms in Echinodermata:
No other group of animals has such
complicated metamorphosis in the course of
development. Development may be direct or
indirect. In direct one, the larval stages are missing
while in indirect one, various types of free
swimming larvae are formed. In each class, a few
members, are viviparous, that is, they brood their
young in a sort of brood pouch on the surface of
their body. The development of larva takes place in
a typical deuterostomous fashion. In most cases
the characteristic free swimming larvae developed
externally which are of phylogenetic significance.

44. (a) Bipinnaria larva:
Two types of development occur in asteroids. The
direct type has large, yolky eggs and a free swimming larval stage.
The indirect stage has homolecithal eggs with little yolk and a free
swimming larval stage. After hatching the larva develops cilia and
begins a free swimming life. The larva feeds on diatoms as an
alimentary canal is formed. The presence of powerful ciliary band on
the stomodaeal walls help in feeding. Two lateral longitudinal
locomotory ciliated bands develop which connect in front of mouth,
forming a preoral loop and in front of the annus, to form a preoral
loop. Preoral loop later separates or in some cases develops
independently into an anterior ciliated ring around the body. Three
lobe sor projections are also develop on each side of the body
bordered by ciliary bands. This larva is known as bipinnaria and
develops in 2 to 7 days.
(b) Brachiolaria larva:
Bipinnairia larva transforms into brachiolaria larva which
develops three short arms at preoral lobe, known as brachiolar arms.
They contain coelomic extensions and adhesive cells at their tips. An
adhesive glandular area at their base acts as a sucker. Appearance of

45. [II] Class 2: Ophiuroidea
Ophiopluteus larva:
Pluteus is the free swimming larva in brittle star s which
is known as ophiopluteus. It is similar to echinopluteus of
echinoids with the only difference that the former has fewer
arms than the later. The posterolateral arms are the longest
and directed forward. After gastrulation the arms develop
gradually. Posterolateral arms are form first. After 4, 10 and 18
days, anterolateral, postoral and posterodorsal arms develop,
respectively. Ciliated bands accompany the arms edges.
Internally the larva contains coelomic chambers and
archenteron. Internal development proceeds in the same way
as in other classes. While free swimming metamorphosis of the
larva starts, there being no attachment stage. Tiny serpent star
sinks to the bottom to begin its adult existence.

46. [III] Class 3: Echinoidea:
Echinopluteus larva:
Larva is formed after gastrulation. Gastrula
becomes conical, one side of which flatters to form
the oral surface. Stomodaeal invagination
communicates with archenteron and the gut is
differentiated into mouth, oesophagus, stomach and
intestine. Blastopore remains as larval annus. Larva
begins to form projections which develop into arms.
There are six arms namely, preoral, anterolateral,
anterodorsal, postoral, posterodorsal and
posterolaeral.

47. [IV] Class 4: Holothuroidea
(a) Auricularia larva:
After gastrulation and formation of coelomic sacs
and gut, the embryo becomes a free swimming larva
called auricularia larva, within three days. It is transparent,
pelagic about 0.5 to 1 mm in length. It swims about by a
ciliated band which forms preoral loop and an anal loop.
Internally, larva has a curved gut with sacciform
stomach, hydrocoel and right and left stomatocoels.
Some giant auricularians of unknown adults
reported from Bermuda, Japan and Canary Islands
measure about 15mm in length and possess a frilly
flagellated band.

48. (b) Doliolaria larva:
It is a transitional stage from auricularia and appears
barrel-shaped and alike doliolaria of crinoids. Continuous
ciliated band breaks in 3 to 5 flagellated rings. Mouth is
shifted to anterior and annus to posterior pole.
Metamorphosis is gradual during which it acquires 5
tentacles and 1 to 2functional podia. As such it is
sometimes known as pentactula. After appearance of
more podia and tentacles, sea cucumber settles to the sea
bottom and leads an adult mode of life.

49.  [V] Class 5: Crinoidea
 (a) Doliolaria larva:
 It hatches as a free swimming larva. Body has
4 to 5 ciliated bands with an apical sensory
plate at the anterior end provided with a bunch
of cilia. There is an adhesive pit over the first
ciliated band, near the apical plate in the mid
ventral line. Between second and third ciliated
band lies the stomodaeum or vestibule.
Skeleton also develops at this larval stage.
After the differentiation into prospective organs,
larva attaches itself and internal organs rotate
at an angle of 90 degrees from ventral to
posterior position. Larva forms a stalk and is
now referred as cystidean or pentacrinoid larva
which, after sometime metamorphoses into

50. Economic Importance of Echinodermata:
The economic importance of Echinoderms is considerable to
man. Of all echinoderms the star fish and sea cucumber are
of much economic value to man.
 The dried skeleton of echinoderms have been crushed and
utilized as fertilizer on ground.
 Echinoderms are quite rich in calcium and nitrogenous
content so that they are used as food and lime supply four
poultry.
 Among the Pacific Island, South Pacific Ocean and China,
sea cucumbers are used as food by man. They are boiled
and dried in the sun and sold in the market. In America sea
cucumber has been used especially in soup for several
years.

51.  The ovaries of sea urchins and the eggs of starfish are
eaten, either raw or cooked by the Europeans as well as
by the people of tropical regions of South America and the
Mediterranean. Sea urchins are also used in research
particularly as model in development biology and other
sections of science.
 Starfish, urchins and cucumber are good scavengers. The
latter are perpetually ingesting mud and sediment of the
sea bottom the contained organic food, thus helping in the
decomposition processed of the organic material
continuously accumulating at the sea bottom. Their food
includes seaweeds, small crustaceans, mollusks, tube
worms, small animals matter and other small organisms
and bottom debris. It has been said that an ocean without
echinoderms might become a putrid cesspool.
 Natives of the Pacific Islands use juices from the body wall
of certain sea cucumbers to poison fish in tidal pools.

52. Negative Aspects:
 The star fish are of particular concern to man as
they destroy clams oysters and other marine
mollusks that serve as human food.
 A star fish in aquarium devours nearly 10 oysters
or clams in a day. They are universally hated by
oyster and clean fisherman because of
tremendous damages they do to those
commercially important food animals each year.