for Bsc agriculture students

1. Lecture 2
Nematode Morphology
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2. Topics
 Size
 Shape
 Body wall (Outer body tube)
 Digestive system (inner body tube)
 Reproductive system
 Excretory system
 Nervous system
 Respiratory and Circulatory systems
 Definition
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3. Size
 Human and Animal parasites are big and visible
to the naked eyes
 Ascaris lumbricoides …………………...30 cm
 Dracunculus medinensis……………….1m
 Placentonema gigantissimma ………...8 m (longest)
 Free-living nematodes microscopic
 Greeffiella minutum…………………….82 µm (smallest)
 Plant parasitic nematodes
 Microscopic, range……………………..0.3 – 2.0 mm
 Paralongidorus epimikis ……………1.2 cm (longest)
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4. Relative Size & Shape
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5. Shape
Normal shape
Vermiform Sexual dimorphism
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6. Body regions, Colouration, Segmentation
 Head – Continuous or set off
 Tail - body portion beyond anus,
shapes variable
 Appendageless
 Colourless
 Body wall transparent
 No metameric segmentation
 All natural openings on one side
- ventral side
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7. Body Organization and Symmetry
 Body tubular
 Outer tube – Body wall
 Inner tube – Alimentary canal
 Body Cavity – Pseudocoelome
 Bilateral symmetry
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8. Body Wall
1. Cuticle 2. Hypodermis 3. Muscle layer
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9. Cuticle
– Non-cellular
– Tough but elastic
– Exoskeleton
– Regulates permeability
– Regulates body growth
– Helps in locomotion
– Plays role in respiration
– Plays role in excretion
– Moults four times
– Consists of structural proteins
(keratin, collagen, matricin)
– Chitin absent in cuticle
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10. Cuticular markings
A.Transverse
Smooth Striated Annulated
Striated Annulated
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11. Cuticular markings
Caudal alae (Bursa)
Leptoderan Peloderan
B. Longitudinal
Lateral alae
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12. Hypodermis & Musculature
Hypodermis: Cellular or syncytial, secretes new cuticle after every moult,
forms 4 hypodermal chords
Musculature : Somatic, Specialized
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13. Musculature
 Somatic muscles
Attached to body wall
Nvbnvbn
• Specialized muscles
Associated with special organs e.g., stylet, spicules
A. Platymyarian B. Coelomyarian C. Circomyarian
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14. Alimentary Canal – The Inner Body Tube
 Stomodaeum – The Fore gut
 Oral aperture (Mouth)
 Stoma ( Buccal cavity)
 Oesophagus (Pharynx)
 Cardia (Oesophago-intestinal valve)
 Mesenteron – The Mid gut
 Intestine
 Proctodaeum – The Hind gut
 Rectum
 Anus
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15. Stomodaeum - Oral aperture
En-face view
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16. Microbivorous Predator Phytophagous
Stomodaeum - Stoma
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17. Cephalic Sclerotization & Stylet
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18. Stomodaeum - The Stylet
Stomatostylets in Tylenchids
Conus
Shaft
Knobs(3)
Lumen
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19. Stomodaeum - The Oesophagus
Corpus
Postcorpus
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20. Stomodaeum - PPNs
No Gland overlap Gland overlap
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21. Feeding Tube
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22. The Mesenteron and Proctodaeum
Mesenteron
Intestine
Wall made up of single layer
of epithelial cells;
inner margins lined with microvilli
Proctodaeum
Rectum
In males, intestine joins vas deferens
to form common tube – cloaca
Anus
Females have a separate opening;
pore-like on ventral side
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23. Reproductive System
 Nematodes are dioecious
 Both sexes look alike
 Reproductive system is tubular
 Males v/s Females
• Males are slightly shorter
• Tail end curved ventrally
• Possess secondary sexual organs
• Spicules
• Gubernaculum
• Bursa
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24. Female Reproductive System
Ovary
Germinal zone: Production of oogonia
Growth zone: Oogonia increase in size
Oviduct
A narrow passage for oogonia
Spermatheca
Store sperms; oogonia get fertilized
when pass through
Uterus
Columellar glandular cells – deposit
egg shell around fertilized egg
Vagina
Expulsion of egg
Vulva
Slit-like on ventral side; help in egg
laying and copulation
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25. Female Reproductive System
Terminology
No. of genital tracts
• Monodelphic
One
• Didelphic
Two
Direction of genital tracts
• Prodelphic
Directed anteriorly
• Opisthodelphic
Directed posteriorly
• Amphidelphic
One directed anteriorly,
second posteriorly
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26. Male Reproductive System
Testis
Production of spermatogonia
Seminal vesicle
Storage of sperms till mating
Vas Deferens
Passage for sperms, merges with intestine
to form cloaca
Cloaca
Common tube for digestive and
reproductive systems
Cloacal aperture
Common opening for both systems
Spicules
Sclerotized, a pair, movable, mating organ
Gubernaculum
Plate-like, not movable, guides the
movement of spicules
Bursa
External cuticular extensions on lateral side, a pair,
leptoderan or peloderan, hold female during mating
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27. Excretory System
Phylum Nematoda divided into two classes based on the type of excretory system
Function speculatory, may be secretory, osmotic regulation etc.
Canalicular or Tubular type
Present in Class Secernentea
Basically H–shaped, variable
Two main longitudinal excretory ducts running
in lateral hypodermal chords
Joined in oesophageal region by a transverse duct
A terminal duct arises and opens on ventral side -
the excretory pore
Glandular type
Present in Class Adenophorea
Single (Renette) cell leads to an excretory duct
and opens outside through pore
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28. Nervous System
• Main nerve centre (Brain)
is a ring called Nerve Ring
or Circum-oesophageal commissure
encircling the isthmus region of
oesophagus
• Main nerves arise from nerve ring
and run anteriorly and posteriorly
in the hypodermal chords
• These longitudinal nerves are
interconnected at regular intervals
throughout length
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29. Sense organs
• Chemoreceptors
(to perceive the sense of chemicals in vicinity)
Amphids
A pair, opening on lateral sides in head region,
help in locating plant roots
(Host finding/Chemotaxis)
Phasmids
A pair, opening on lateral sides in tail region,
enlarged phasmids are called Scutellae
• Tactoreceptors
(to perceive the sense of touch)
Papillae/Setae
Cephalic
Cervical
Caudal
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30. Other Systems
 Respiratory System
 Well developed organs lacking
 Oxygen required for aerobic PPNs diffuses through
cuticle
 Circulatory System
 Well developed organs lacking
 Pseudocoelomic fluid serves as the means of transport
since it bathes different organs
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31. Definition
Nematodes are triploblastic,
bilaterally symmetrical,
unsegmented,
pseudoceolomate invertebrates,
with four main hypodermal chords,
a triradiate oesophagus,
circum-oesophageal nerve ring,
and lacking specialized organs for
respiration and circulation;
they have tubular gonads
which open separately in females
but join alimentary canal in males
to open through a cloacal aperture.
Gross Morphology
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