21. phylum nematoda full explanation only on slide share

1. PHYLUM NEMATODA
By
SYED SHAKEEL SHAH
Department of Zoology
University of Narowal

2. Phylum Nematoda
• Round or Thread worms
• size 1-2 mm mostly but some may reach 60 cm or more
• Pseudocoelomates
• non-sigmented
• Free living and parasitic species
• Pointed at both ends
• Covered by a thick multilayered cuticle (non-cellular covering)
• Epidermis is syncytial (secretes cuticle)
2

3. Nematode life cycle
• Cuticle is
shed 4
times
during
develop
ment
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4. Musculature
• Lack circular muscles
• muscular layer (longitudinal muscles) that arrange in 4
groups separated by the dorsal, ventral and lateral
hypodermal chords, each muscle cell connected to either
the dorsal or ventral nerve chord by muscle cell process;

5. Movement and hydrostatic skeleton
• Movement is by thrashing the
body into sinusoidal waves
generated by alternating
contraction of longitudinal
muscles on each side of the
body.
• The round shape of nematodes
is due to the hydrostatic
pressure generated by
celoemic fluid and its opposing
rigid cuticle.

6. Nervous system
• Nervous system made of brain (nerve ring and associated
ganglia and at least 4 longitudinal nerves that run in the
dorsal, ventral and lateral nerve chords in the hypodermis
• Sense organs include a pair of head chemoreceptive
amphids (characteristic feature of all nematodes), other
sense organs found in certain groups include: posteriorly
located chemoreceptive phasmids, ocelli, cephalic and
caudal papillae as well as mechanoceptors

7. 7
Nematode Features
• Eutely: Cell number in adult tissue remain constant throughout
life so that the limited increase in size is a function of increase in
cell size NOT number).
• Tubes within tubes worms, all organ systems tubular;

8. Nematode Features
• Digestive system complete with mouth, muscular pharynx
(esophagous), intestine and rectum;
• Excretory system made of renette glandular cells in most spp;
• No specialized gas exchange or circulatory system.
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9. 9
Nematode Reproduction & Life Cycle
• Worms are mostly dioecious;
• Male reproductive system tubular and made of testis, vas
deferens, ejaculatory duct that opens in cloaca, many spp. have
bursa and 1-2 copulatory spicules;
• Female reproductive system tubular and made of one or two
ovaries, each leads into oviduct--seminal receptacle—uterus, a
vulva leads to female gonopore.
• Fertilization internal following copulation or hypodermic
impregnation;
• Females are oviparous, ovo-viviparous or viviparous;
• L.C. involves ecdysis of larval stages controlled by molting
hormones with 4 larval stages before worms become adults; some
larval stages can molt within the egg shell; Parasitic stages mostly
use the third larval stage (L-3) as infective stage to the final host..

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11. Classification of parasitic Nematodes
• Class Chromadorea
(3 sub-classes) Sub-class: Rhabditia
• Orders: 1. Rhabditida –
• 2. Strongylida - Ancylostoma (hookworm), Enterobius (pin
worm)
– Sub-class: Spiruria –
• Orders: 1. Spirurida - Filarioidea - filarial worms. Wuchereria
bancrofti (elephantiasis), Onchocerca volvulus (river
blindness), Dirofilaria immitis (dog heartworm).
• 2. Ascaridida - intestinal parasites of vertebrates. Ascaris.
Ascaris, Toxocara canis (dog ascarid)

12. Debilitating effect of parasitic
Nematodes
• Blood suction. E.g Hook worms
– Suck about 0.6 ml blood/day
– 100 worms= 60 ml/day= 180 ml/month
• Blocking of intestine and bile ducts. E.g ascaris
– In cases of heavy infection.
• Blocking of blood or lymphatic system. E.g
Filaria
– Elephantiasis as in Onchocerca volnulus

13. Trichuris trichura L.C.
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14. Hookworm L.C.
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15. A. Lumbricoides L. C.
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16. E. vermicularis L.C.
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17. O. volvulus L.C.
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18. Wuchereria bancrofti L.C.
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19. Thank You…!