Nematodes Classification MODULE
Microbiology
43
Notes
NEMATODES CLASSIFICATION
46.1 INTRODUCTION
Nematodes belong to the phylum Nematoda. Many species of nematodes are free
living in fresh or salt water, mud or soil. They are parasites of both animals and
plants. Only medically important nematodes are discussed in the following
sections.
OBJECTIVES
After reading this lesson, you will be able to:
z explain the general characteristics of nematodes
z describe the classification of nematodes
General characteristics
Nematodes are elongated, cylindrical, bilaterally symmetrical, unsegmented
worms with tapering ends. The name ‘ nematodes’ means thread like. The body
is covered with tough cuticle.
Their size varies from less than 5 mm (Trichinella spiralis) to 1 metre
(Dracunculus medinensis). The male is generally smaller than female and its
posterior end is curved or coiled ventrally. The sexes are separate. Female
nematodes may be divided as
Oviparous (nematodes which lay eggs)
z Laying unsegmented eggs
o Ascaris lumbricoides
o Trichuris trichura
z Laying eggs with segmented ova
MICROBIOLOGY 381
MODULE Nematodes Classification
Microbiology o Ancylostoma duodenale
o Necator americanus
Viviparous (nematodes which give birth to larvae)
z Dracunculus medinensis
z Wucheria bancrofti
Notes Ovo- viviparous (nematodes laying eggs containing larvae that immediately
hatch out)
z Strongyloides stercoralis
Modes of infection with nematode parasites
Ingestion of food and water contaminated with eggs (Ascaris lumbricoides),
ingestion of cyclops (Dracunculus medinensis) or ingestion of infected pork
(Trichinella spiralis). Penetration of skin for example larvae of A. duodenale,
N. americanus and S. stercoralis. Blood sucking insects for example Wucheria
bancrofti and Brugia malayi.
Classification of nematodes on the basis of habitat of adult worms:
Intestinal
Small intestine: A. lumbricoides, A. duedenale, N.americanus, S.stercoraris, T.
spiralis.
Large intestine: E. vermicularis, T. trichuria.
Somatic
Lymphatic system: W. bancrofti, B. malayi.
Subcutaneous tissue: Loa loa, Onchocerca volvulus, D. medinensis.
Body cavity: Mansonella perstans.
Conjunctiva: Loa loa.
INTEXT QUESTIONS 43.1
1. Which of the following nematodes is ovoviviparous?
(a) Ascaris lumbricoides.
(b) Dracunculus medinensis.
382 MICROBIOLOGY
Nematodes Classification MODULE
(c) Strongyloides stercoralis. Microbiology
(d) Trichinella spiralis.
2. Which of the following nematodes lays unsegmented eggs?
(a) Necator americanus.
(b) Trichuris trichiura.
(c) Strongyloides stercoralis.. Notes
(d) Trichinella spiralis
3. Which of the following nematodes lays eggs containing larvae?
(a) Trichinella spiralis.
(b) Enterobius vermicularis.
(c) Brugia malayi.
(d) Ascaris lumbricoides.
4. Adult worm of which of the following resides in human body cavity?
(a) Wucheria bancrofti.
(b) Brugia malayi.
(c) Ascaris lumbricoides.
(d) Mansonella perstans.
5. Adult worm of which of the following resides in large intestine?
(a) Ascaris lumbricoides.
(b) Dracunculus medinensis.
(c) Strongyloides stercoralis.
(d) Enterobius vermicularis.
WHAT YOU HAVE LEARNT
z Nematodes are elongated, cylindrical, bilaterally symmetrical, unsegmented
worms with tapering ends. Sexes are separate into male and female. Female
nematodes may be divided as oviparous, ovi viviparous and viviparous.
Nematodes have different modes of infection like, by ingestion of food and
water contaminated by eggs of nematodes, ingestion of and infected pork,
penetration of skin and bite of blood sucking insects. Nematodes can be
classified on the basis of habitat of adult worms.
MICROBIOLOGY 383
MODULE Nematodes Classification
Microbiology
TERMINAL QUESTION
1. Classify nematodes?
Notes ANSWERS OF INTEXT QUESTIONS
43.1
1. (c)
2. (b)
3. (b)
4. (d)
5. (d)
384 MICROBIOLOGY
