Difference between revisions of "Nematodes"

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== Introduction ==
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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''')
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**a '''buccal cavity'''
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**'''teeth''' or '''cutting plates'''.
 +
 +
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=== Feeding Habits ===
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*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!
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 +
 +
 
'''Superfamilies:'''
 
'''Superfamilies:'''
  

Revision as of 00:11, 23 December 2008

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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


Occlusion of pancreatic ducts sometimes happens Pancreas Parasitic - Pathology