Nematode Structure and Function

Recognition Features

• A unique feature of the nematodes is that the fluid in the body cavity is maintained under high pressure (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 these differ in shape and size between species, they are very useful in 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

Mononchidae eating a Mononchidae - Wikimedia Commons

• 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