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General Morphology of Nematodes
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Muscles
Somatic
musculature. Beneath the hypodermis, a single layer of cells, more or
less spindle shaped, longitudinally oriented, and attached to the
hypodermis throughout its length, comprise the somatic {musculature. It
is divided by longitudinal chords into longitudinal fields. The cells
are arranged in rows of two, four or more and are variable in number.
Earlier, the number of cells was considered to be of some taxonomic
value but because of the fact these are quite variable in number, these
are not considered to be of any taxonomic value. Based on the number of
muscles cells in each quadrant, the nematodes have been classified
mainly in two categories, meromyarian and polymyarian. Meromyarian is
applied to the condition wherein only two to four longitudinal rows of
muscles are present between the chords as against the other category (polymyarian)
where large numbers of muscle rows (six or more) are present in each
field. A third category, not used now, exists in earlier literature
under the name holomyarian which incorporated those nematodes where the
muscle layer was divided into two fields or was continuous because of
presence of only two chords or no chords at all.
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The
musculature helps in the movement of the nematode by contracting and
relaxing in the anterior as well as the posterior planes. The turgor
pressure of the body contents and the elasticity of the cuticle
oppose the contraction of the muscles. Waves of such contraction in
the opposite plane, in the dorsal and ventral musculature,
result id the typical
serpentine movement of the nematode body.
The
muscle cells are spindle or rhomboid shaped and consists of two
zones, sacroplasmic and fibrillar. The former contains the nucleus
and fibrillar network and in the latter, ribbon like fibres,
separated from each other by sacroplasm, are present. Two types of
muscle cells are recognized. When the ribbon-like fibres are present
only on the side of the muscle cell, next to the hypodermis, it is
referred to as platymyarian muscle cells. When the fibres extend to
the sides of the muscle cells, partly enclosing the sacroplasm, then
these are called coelomyarian muscle cells. However, various inter
grades may be encountered between these two types of muscle cells
but generally, nematodes having meromyarian muscle system have cells
of platymyarian type and the polymyarian types have coelomyarian
muscle cells. |
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Specialised muscles. In addition
to the general 1)ody musculature, whereby motility and progression are
affected, there are various special muscles such as those connected with
anus, vulva, retractile muscles of the spicules and specialized muscles
present in the male tail, which facilitate copulation.
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