Transcript Lecture Slides for Biology of Hirudinea (ZLY 201)

HIRUDO
Basic Invertebrate
Zoology (ZLY 201)
Delivered by
SHITTU, O.
Dept. of Zoology,
University of Ilorin,
Nigeria
General Characteristics
• 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
• 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).
• Some are predacious with suckers for anchorage.
• 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)
Ventral View of the Anterior Sucker
Showing the 3 Jaws
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.
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.
 They prefer muddy freshwater pools and ditches
with large weed growth in the temperate.
 Eggs are laid outside water during spring &
summer months.
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.
Taxonomy of Hirudinea
Phylum
Annelida
Subphylum
Class
Subclass
Infraclass
Order
Family
Clitellata
Hirudinea
Hirudinea Lamarck, 1818 –
leeches,
Euhirudinea Lukin, 1956
Arhynchobdellida Blanchard,
1894
Hirudinidae Whitman, 1886
Subfamily Hirudinariinae Whitman,
1886
Genus Hirudo Linnaeus, 1758
Species Hirudo medicinalis Linnaeus,
1758
Morphology
• When the animal is stretched,
it appears convex dorsally
and flat ventrally.
Annulus
Eye position of the leech species Hirudo
medicinalis and Haemopis sanguisuga.
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.
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
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:-
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.
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.
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)
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
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.
Ventral Dissection of the mouth Showing
Jaws in Biting Position
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
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 (heartshaped) at segment XIX and runs backward between the
last pair of crop diverticula (XXIII) and leads to the
rectum.
The Gut
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.
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.
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
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.
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.
Reproductive
System (Male)
• Testes in 10 pairs of
coelomic sacs (XII –
XXI)
• Short vasa deferentia
connects testis to the
vd of each side.
• At XI, they enlarge
and coil to form a
storage organ called
epididymis/sperm
vesicles.
• Followed by thick
walled ejaculatory
ducts leading to the
artrium.
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).
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.
Reproductive
System (Female)
• The oviduct leads to a Ushaped 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
head.
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
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
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
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
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
 Lateral sinuses have muscular walls and
nerve cord &
are responsible for circulating blood.
– 1 posterior
 Three main branches originated and are:
ganglionic masses
 the latero-dorsals,
– 2 lateral sinuses.
 latero-ventrals and
 latero-laterals.
Circulation
(Blood System)
Reconstruction
coelomic sinus
Hirudo
of
the
system of
• The blood consists of:– a plasma, coloured red by haemoglobin in solution and
– various amoeboid corpuscles
– together with some chloragogenous cells.
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
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
circumpharyngeal
nerve
ring.
Arthropods have several
segmental ganglia which
contribute to the brain
Histology
Transverse Section of H. medicinalis in the intestinal region
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).
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)
Histology
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.
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.
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.
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.
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.
End of Hirudinea Slides