Difference between revisions of "Nematodes"
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| + | == 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. | ||
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| + | == 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'''. | ||
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| + | |||
| + | === 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! | ||
| + | |||
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'''Superfamilies:''' | '''Superfamilies:''' | ||
Revision as of 00:11, 23 December 2008
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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
- Ancylostomatoidea (Hook worms)
NON-BURSATE
Occlusion of pancreatic ducts sometimes happens Pancreas Parasitic - Pathology