Type study

1. HIRUDO
By
Dr. Priti D.Diwan
Assistant Professor
Department of Zoology
J.D.Patil Sangludkar Mahavidyalay Daryapur.

2. • Hirudinea comprises leeches which occur more in
tropical regions than temperate regions.
• Leeches inhabit a wide variety of habitations ranging
from freshwater, marine and terrestrial ecosystems.
• About 300 species of Hirudinea abound worldwide.
• They vary in length between 2 and 30cm.
• The most specialized Annelids which are advanced in
forms than the Oligochaetes.
• They have lost their parapodia (false feet) and setae.
General Characteristics

3. General Characteristics
• Swimming by vertical undulations or loops by
using its suckers to grip surfaces.
• They exhibit variation in patterns and colours.
• They are dorso-ventrally flattened.
• Most leeches are ectoparasites (haematophagus,
sanguivorous)..
• The gut is adapted for storage of large quantities
of blood.
• Mouth opens at the base of the anterior sucker, has
3 half-moon-shaped jaws (Next Slide)

4. Ventral View of the Anterior Sucker
Showing the 3 Jaws

5. General Characteristics
• leeches lack distinct coelomic compartments.
• In some species, the septa have disappeared, and
the coelomic cavity is filled with connective tissue
and a system of spaces called lacunae.
• The coelomic lacunae form a regular system of
channels filled with coelomic fluid serving as an
auxiliary circulatory system.
• Hermaphroditic, possessing temporary clitellum
(only during breeding).
• The clitellum secretes cocoon for reception and
storage of eggs.

6. Ecology of Hirudinea
 700 species of leeches are currently recognized
 100 are marine, 90 terrestrial and the remainder
freshwater.
 The Indian cattle Leech H. granulosus, lives in
ponds, lakes, swamps and slow moving streams.
 H. medicinalis lives mainly in stagnant waters of
marshes and ponds with a muddy substrate.
.
 Eggs are laid outside water during spring &
summer months.

7. Ecology of Hirudinea
 H. medicinalis requires relatively warm water
(19-23ºC) in which to feed and breed.
 Egg cocoons are laid on marginal plants.
 They feed on the blood of vertebrates and it is
thought that mammalian or possibly avian blood
is required to enable successful breeding.

8. Taxonomy of Hirudinea
Phylum Annelida
Subphylum Clitellata
Class Hirudinea
Subclass Hirudinea Lamarck, 1818 –
leeches,
Infraclass Euhirudinea Lukin, 1956
Order Arhynchobdellida Blanchard,
1894
Family Hirudinidae Whitman, 1886
Subfamily Hirudinariinae Whitman,
1886
Genus Hirudo Linnaeus, 1758
Specie
s
Hirudo medicinalis Linnaeus,
1758

9. Morphology
• When the animal is stretched,
it appears convex dorsally and
flat ventrally.
Eye position of the leech species Hirudo
medicinalis and Haemopis sanguisuga.
Annulus

10. Morphology
Shape and Size
Soft, vermiform, elongated and dorso-ventrally
flattened body
Size ranges from 2 to 35cm depending on diet and
species.
The skin is always moistened with mucus and fluid
thereby aiding cutaneous respiration.
The body form is narrowest at the anterior and
broadened at the posterior end.
They exhibit alternation in shape and proportion by
being ribbon shaped when extended and cylindrical
when contracted.

11. External Characters
• A large specimen measures about 12 cm X 1.5 cm
when fully extended, although it may contract to less
than half this length.
• Variable colour pattern:
• May consist of a greenish background with a pair of
longitudinal red stripes and a pattern of irregular
black markings near the lateral margins.
• The ventral surface is usually black with white and
grey markings.
• Leech body is divided by transverse furrows into 102
annuli

12. External Characters
• Typically, mid-body segment comprises 5 annuli
but towards the extremities, the number per
segment progressively decreases.
• The distribution of the annuli between the
prostomium and body segments is as follows:-

13. Externals – Anterior Section
• The anterior sucker is a
depression on the ventral
surface of segment I-IV.
• A small tri-radiate aperture
lies at the base of the
depression.
• The prostomium forms the
anterior border of the
sucker, It turns back
ventrally & partially closes
the oral aperture.

14. Externals – Anterior Section
• The male pore is conspicuous and lies between
annuli 31 & 32, it gives a guide to the female pore,
• The female pore lies five annuli further (36 & 37),
• During the breeding season, the glandular clitellum
appears on annuli 26-40.

15. Externals – Anterior Section
• 3 kinds of principal sense organs abound superficially,
viz;
– Tactile organs: Every annulus has receptor organs raised on
the papillae, they are annular receptors that serve as tactile
organs.
– Segmental receptors/Sensillae (Light sensitive organs):
These are not raised on papillae but located on every fifth
annulus within white circular areas. (Internal segmentation).
– Larger light sensitive cells: found on segments I-V, 5 pairs
of eyes backed by a pigmented cup (black dots)

16. Externals – Posterior Section
• The posterior sucker is a
muscular disc (circular).
• It is a more powerful organ of
adhesion than the anterior
sucker.
• It is made up of seven fused
segments.
• The nephridiopores are found
on segment 7 between annuli
14 & 15, and between the 2nd
& 3rd annuli of the following
16 segments.
• The anus is a very small
aperture located on the mid –
dorsal line of the posterior
section. Anus

17. Oral Sucker
• The buccal cavity containing the jaws is separated
from the sucker cavity by low fold velum.
• During feeding the velum retracts backward to allow
the jaws to be pushed forward into the sucker cavity to
ensure adherence with host skin.
• Each jaw is a muscular ridge shaped like a half circular
saw (one median & two ventro-lateral)
• Jaws are covered by cuticle and along the edges forms
a row of minute teeth.
• During incision, muscles holding the jaw rock them so
that the teeth moves with a sawing action.
• This results in a Y – shaped incision.

18. Ventral Dissection of the mouth Showing
Jaws in Biting Position

19. Ventral View of the Anterior Section
Showing the Oral Anatomy
• Each jaw is a
muscular ridge
shaped like a half
circular saw (one
median & two
ventro-lateral)
• Jaws are covered
by cuticle and
along the edges
forms a row of
minute teeth

20. Alimentary Canal
• The oesophagus, a narrow tube behind the pharynx
conveys blood into the crop.
• The crop is the largest part of the leech alimentary canal
and it is adapted for storage of considerable volume of
blood.
• To ensure storage, it is lined with eleven pairs of
diverticula (one pair each on segments VIII –XVIII.
• The last pair runs back to the hind end of the body.
• In segment XVIII, the crop terminates into a narrower
pore leading to the intestine.
• The intestine is thin-walled but slightly swollen (heart-
shaped) at segment XIX and runs backward between the
last pair of crop diverticula (XXIII) and leads to the
rectum.

21. The Gut

22. Digestion
• Numerous unicellular salivary glands open into the
jaws, they secrete anticoagulin.
• Anticoagulin prevents the clotting of host blood
resulting from the wound.
• The blood is sucked into the alimentary canal by the
pumping action of the pharynx (5mm oval sac).
• At rest, pharynx wall are deeply folded but dilated by
radial muscles during feeding running out to the body
wall.
• The space between the radial muscles is completely
filled with salivary gland cells.

23. Digestion
Nutrition in leeches is of interest for several reasons:-
• Typical leeches are blood-sucking ectoparasites, they are
remarkably adept at removing from the host a very
considerable quantity of blood without being noticed. This
requires sharp, precise cutting equipments and the
assistance of a local anaesthetic.
• The blood must be prevented from clotting in the gut, for
during locomotion the leech becomes alternately short and
thick and long and thin and this would be impossible if the
gut contained a mass of clotted blood.
• Finally, a series of investigators failed to identify any
proteolytic enzymes in the gut of Hirudo and it appears that
the function of digestion has been taken over entirely by
symbiotic bacteria.

24. Digestion
• An extract of the head of Hirudo contains a powerful
anticoagulin; hirudin which makes the wound made by
a leech bleeds over time.
• However, Lindemann (1939) found that leech head
extract also contains a histamine like substance capable of
causing the dilatation of capillaries.
• He postulated that this was the substance actually
injected into the wound and that the free flow of blood
was due to the enlargement of the blood vessels rather
than the inhibition of clotting.
• The act of biting and secretion of salivary glands is
divisible into two phases
(i) the biting phase, (ii) the sucking phase

25. Digestion
• Hirudin is an hydrolyzing protein product with empirical
formula of C30H60O20N8 and a molecular weight of 852.
• It probably acts by inhibiting the enzyme thrombokinase
• Only 0-8 mg is required to prevent indefinitely the
coagulation of 5 ml of rabbit blood.
• Leech takes a meal of blood every six months because
digestion is slow.
• Energy consumption is at 15 cal per day at 18°C.
• During starvation the leech utilized the stored
carbohydrates and fats thereby dropping its energy
consumption to about 7 cal per day.

26. Digestion
• When a meal of blood has been sucked into the crop it
first thickens, water being abstracted and passed out via
the nephridia together with considerable quantities of
sodium chloride.
• The haemoglobin soon becomes deoxygenated but the
erythrocytes remain intact for a very long time (Free from
putrefaction).
• Pseudomonas hirudinis is a bacterium that aid blood
protein digestion in Leeches, it does this by transforming
protein into soluble nitrogenous compounds.
• Pseudomonas hirudinis also prevents the growth of other
bacteria thereby retarding putrefaction of the RBC.

27. Reproductive
System
(Male)
• Testes in 10 pairs of coelomic
sacs (XII – XXII)
• posterior part of testis sac
proceeds in small duct called
as vasa efferentia .
• Paired slender longitudinal
tubes situated on either side
called as vasa defferentia
• At X, they enlarge and coil to
form a storage organ called
epididymis/sperm vesicles.
• Short narrow tube arises from
epididymis called as
ejaculatory Duct
• Followed by thick walled
ejaculatory ducts leading to the
artrium in ix and x segment

29. Reproductive
System
(Male)
• Atrium consists of two
parts:-
– a basal bulb covered
with several layers of
unicellular prostate
glands, and
– a penis sheath
surrounding an eversible
muscular penis.
• Spermatogonia bud off
from the walls of the
testis sacs & develop
into spermatozoa
(Coelomic fluid).

30. Reproductive
System (Female)
• Ovaries appear as
elongated cords.
• They have club-shaped
terminations which lie
freely in a single pair of
coelomic sacs in
segment XI.
• Short ducts run from
these to a common
oviduct, which is
closely invested with a
thick layer of
unicellular albumen
glands.

31. Reproductive
System (Female)
• The oviduct leads to a U-
shaped muscular vagina
which in turn opens to the
exterior.
• Ova are budded off from
the cords in the ovisacs,
• When Cross fertilization
takes place, zygote is
coated with albumen in
the oviduct.
• After cocoon formation
by the clitellum, fertilized
eggs pass from the female
pore into the cocoon, the
leech then slips over its

32. Excretory
System
Seventeen pairs of
nephridia opens on VII to
XXIII.
A complete separation of
the funnel from the rest
of the nephridium
(Outstanding).
The funnel is more of
circulatory than excretory.
Nephridium is totally
enclosed within a blood
filled Sinus lying on top
of a central
capsule/reservoir
The parts of a typical
Nephridium as seen
in situ

33. Excretory
System
The central capsule is
studded with many small
ciliated funnels.
The central capsule is the
site of formation of
corpuscles for the
coelomic circulatory
system.
The cilia in the funnel
beats outwards wafting
the corpuscles into the
blood.
A winding intra-cellular
canal from the testis sac
follows to the main body
of the nephridium.
The parts of a typical
Nephridium as seen
in situ

34. Excretory
System
The nephridium’s
glandular part originated
from the nephridioblast
which earlier cut off from
ecto-mesoderm.
The vesicle & its duct to
the exterior are
ectodermal.
The nephridium is
enriched with branches of
blood sinus system,
therefore, excretory
products are derived
within rather than from
ciliated organ.
The parts of a typical
Nephridium as seen
in situ

36. Excretory
System
The first six, and the
last pair of nephridia
are not associated with
testes.
Absence of ciliated
organ in nephridia 1st
six & last pair, and the
initial lobe ends blindly
a little away from the
ventral nerve cord
The parts of a typical
Nephridium as seen
in situ

37. Circulation
(Blood System)
• Hirudo has no trace
of blood vessels
unlike Glossiphonia
• 4 main longitudinal
sinuses, viz:
– 1 dorsal above the
gut,
– 1 ventral
containing the
nerve cord &
– 1 posterior
ganglionic masses
– 2 lateral sinuses.
Lateral sinuses have muscular walls and are
responsible for circulating blood.
Three main branches originated and are:
the latero-dorsals,
latero-ventrals and
latero-laterals.

39. Circulation
(Blood System)
• The blood consists of:-
– a plasma, coloured red by haemoglobin in solution and
– various amoeboid corpuscles
– together with some chloragogenous cells.
Reconstruction of the
coelomic sinus system of
Hirudo

40. Nervous System
• The 1st six ganglion
pair consists of 6
capsules dorsal to the
gut.
• The 2nd consists of 3
capsules on each side
of the gut.
• The remaining 4 pairs
of ganglia form the
ventral mass.
• One pair of ganglion
encircled round the
pharynx & closely
associated with
prostomial ganglia.
A contrast from
earthworm, the cerebral
ganglion buried under the
oesophagus is a single
ganglion pair associated
with the prostomium

41. Nervous System
• There are seven
peripheral nerves in
the head region,
• The sympathetic
(stomatogastric)
nervous system(SNS)
consists of nerve a ring
lying on the wall of the
pharynx.
• The SNS links with
the central nervous
system at two points
on the circum-
pharyngeal nerve ring.
Arthropods have several
segmental ganglia which
contribute to the brain

42. Histology
Transverse Section of H. medicinalis in the intestinal region

43. Histology
• The cuticle on the outer surface is secreted by epidermal
cells and renewed at daily intervals
• Epidermal cells are columnar with pentagonal heads
touching neighbouring cells.
• The inner ends are cylindrical with spaces penetrated by
blood capillaries, nerve endings, pigment cells & dermal
fibres.
• Various unicellular glands also originate from the
epidermis (mucus, pear-shaped, elongated tubular).
• The anterior (head) region has mainly pear-shaped
glandular cells which secretes to the surface of the
anterior sucker (Similar to posterior sucker).

44. Histology
• The salivary glands lying between the pharynx and
the body wall are modified epidermal cells.
• They are unicellular, pyriform glands with ductules
leading to the jaws.
• The jaw epidermis of the jaws secretes cuticle which
bears the apertures of these modified epidermal
glands
• The clitellar region has mucus glands, chitogenous
glands found within the circular muscles (secrete
outer casing), albumen glands (longitudinal muscles)

45. Histology

46. Histology
Botryoidal and Vaso-fibrous tissue
• Botryoidal tissue: found between the gut and the muscles
of the body wall.
• It is characteristic of jawed leeches (resembles bunches of
grapes).
• It consists of a network of very fine capillary channels of
the coelomic blood sinus system, lined by swollen
globular cells which are heavily laden with brown
pigment.
• Function
• They correspond to chloragogen tissues and serves as a
center for synthesis of glycogen and fat, a function
roughly equivalent to that of liver cells.

47. Histology
Botryoidal and Vaso-fibrous tissue
• Vaso-fibrous tissue: consists of strands running in the
connective tissue which contain deposits of brown
pigment. They have a small lumen which is continuous
with that of the botryoidal tissue.
• Function
• It is thought that the vaso-fibrous tissue accumulates
excretory products and is in some way complementary to
the botryoidal tissue.

48. Leeches & Medicine
Today, doctors use leeches for:-
 treating abscesses,
 painful joints,
 glaucoma,
 myasthenia,
 to heal venous diseases and thrombosis,
 used in plastic surgery, for improving brain circulation
and
 For curing infertility,
 in the treatment of children with cerebral palsy.
 May treat the following in the future:-multiple sclerosis,
effects of stroke, Parkinson's disease and Alzheimer's.

49. Hirudin
 Hirudin is an anticoagulant that is a polypeptide of 65-66
amino acids.
 Hirudin is the strongest direct specific inhibitor of
thrombin. Quickly reacting with thrombin, forming an
inactive complex.
 Thus, hirudin called "linking all the active sites of
thrombin, can completely inhibit its proteolytic activity,
inhibits the conversion of fibrinogen to fibrin and
activates factors hemocoagulation.

50. Hirudin
 Clinical studies have established the effectiveness of
hirudin as an antithrombotic agent. It has two
advantages over drugs of heparin:
More stable anticoagulant effect;
1. Inhibition of thrombin contained in blood.
2. In addition, the effect of hirudin does not require the
presence of anti-thrombin III or other endogenous
cofactors.
 Leeches have action against coagulation, resolving blood
clots, prevent their formation, stop hemoptysis. They
have antiatherosclerotic and anesthetic action, help
cleanse the body of toxins and poisonous substances.

51. End of Hirudinea
Slides