Nematodes

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PARASITES



Introduction

Nematodes are one of the most prolific life-forms on this planet. Most are free-living, with species adapted to every imaginable habitat. Some are parasitic on plants, and others on animals. The animal parasitic nematodes form a large and diverse array of organisms.


The Nematodes

Recognition Features

  • A unique feature of the nematodes is that the fluid in the body cavity is maintained under high pressue (this is why nematodes often burst after collection).
  • They therefore have a tough elastic cuticle which often forms elaborate structures useful for identification.
  • A muscular pharynx is needed to pump food into the intestine.
  • The shape of the pharynx is characteristic in some groups.
  • There is a nerve ring around the pharynx and four longitudinal nerves with ganglia that co-ordinate movement (many anthelmintics act by disrupting neuromuscular co-ordination).
  • The sexes are separate:
    • the female tail generally ends in a blunt point
    • males usually have two chitinous rods that can be protruded through the cloaca to hold the female - these are called spicules and, being chitinous, are easily seen under the microscope. As they differ in shape and size between species, they are very useful for identification.
  • The bursate nematodes are characterised by a large expansion of the cuticle of the male tail to form a clasping organ (the bursa).
  • Other modifications of the cuticle on both male and female nematodes useful for identification include:
    • alae (wing-like protrusions)
    • vesicles (swellings around the whole circumference of the body).
  • The heads of some nematodes have structures such as:
    • leaf-like lips around the mouth (the leaf-crown)
    • a buccal cavity
    • teeth or cutting plates.


Feeding Habits

  • Many intestinal nematodes are closely applied to the mucosal surface.
  • Some swallow ingesta and/or host secretions.
  • Others suck a plug of mucosa into the buccal cavity (plug feeders), leaving a circular ulcer.
  • Yet others bury their heads deep into the mucosa and suck blood.


General Life-Cycle

  • The basic life-cycle is very simple:

egg → L1 → L2 → L3 → L4 → adult

  • With a moult in between each larval stage.
  • But there are many variations on this theme!


Superfamilies:


BURSATE

NON-BURSATE


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