971
edits
Changes
Jump to navigation
Jump to search
no edit summary
}}
}}
<br>
<br>
== 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:'''
'''Superfamilies:'''