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Comparative studies of natural groups of organisms

3.7.2 Phylum Nematoda organs; movement is by undulating bodies
Task 3.13 in dorso-ventral waves.
Use internet sources and the library
to search for information on phylum Mouth
Nematoda.
Excretory
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Nematodes or roundworms are among pore
the most numerous multicellular animals Female
on earth, and inhabit a wide range of gonopore
environments. They were previously
classified under the phylum Aschelminthes. Lateral Cloaca aperture
Many of them are parasites of animals line
(including humans) and plants. They may Penial spicules
cause serious diseases that are deleterious to Anus Curved tail
human health and agricultural productivity. Straight tail
The free-living species inhabit marine and
freshwater environments, as well as the soils (a) (b)
and sediments in various types of terrestrial Figure 3.44: Structure of Ascaris lumbricoides
biomes. Examples of Nematodes include: (a) female and (b) male
Ascaris lumbricoides (infecting human),
Ascaris squm (infecting pigs), Wuchereria Adaptations of Ascaris to its mode of life
bancrofti (infecting human lymphatic Ascaris possesses some adaptive features
system), hookworms (blood-feeding that enable it to adapt to its parasitic mode
parasite of human and other animals) and of life. These include:
Meloidogyne incognita (plant root knot (a) It has a tough cuticle, which protects it
nematode). from being digested by the enzymes of
the alimentary canal of the host.
Structure of Ascaris sp. (b) It produces chemicals, which act as
Ascaris sp. are round, slender unsegmented anti-enzymes to the digestive enzymes
worms with tapering bodies at both ends. of the host.
They are characterised by being tubes (c) It has an alimentary canal, which opens
within tubes, referring to the alimentary at the mouth and anus. This enables the
canal, which extends from the mouth on the parasite to take food from the hosts’
anterior end to the anus, located near the digestive system.
tail (Figure 3.44). They possess digestive, (d) It possesses digestive enzymes in its
nervous, excretory and reproductive digestive system for the completion of
systems, but they lack distinct circulatory partially digested food from the hosts’
and respiratory systems. The male and alimentary canal.
female Ascaris differ in morphology, as male (e) It has sensory papillae around its
is smaller and more curved at its posterior mouth for detecting food present in the
end than the female. They lack locomotory elementary canal of the host.

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