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Line 1: − {{toplink+ − |backcolour = − |linkpage =Parasites − |linktext =PARASITES − |pagetype=Bugs − }} − <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! − − − === Nematode Eggs === − These vary greatly in appearance and are very useful for diagnosis as they can often be detected and counted in faecal samples. − − NOTE: we use the typical '''strongyle''' egg to provide us with a yard-stick for comparing sizes. A "large egg", for example, means larger than a strongyle egg. A typical strongyle egg is approximately '''80µm''' long. − − − == Nematode Superfamilies == − '''BURSATE''' − − *[[Trichostrongyloidea]] − − *[[Strongyloidea]] − − *[[Ancylostomatoidea]] (Hook worms) − − *[[Metastrongyloidae]] − − NOTE: the Trichostrongyloidea, Strongyloidea and hookworms are very closely related, and are often collectively known as '''"the strongyles"'''. Typically, they produce almost identical eggs, called '''"typical strongyle eggs"'''. − − '''NON-BURSATE''' − − *[[Ascaridoidea]] − − *[[Oxyuroidea]] − − *[[Rhabditoidea]] − − *[[Trichinelloidea]] − − *[[Spiruroidea]] − − *[[Filarioidea]] − − − From the veterinary view-point, the nematodes are most conveniently grouped into '''superfamilies''' because their members often have similar life-cycles and epidemiological features. Superfamily names end in -oidea (the anglicised form is -oid, as in trichostrongyloid). − − − − − − − Occlusion of pancreatic ducts sometimes happens [[Pancreas Parasitic - Pathology]]
Unprotected "Nematodes"
#REDIRECT[[:Category:Nematodes]]
[[Image:Mononchidae eating a Mononchidae.jpg|thumb|right|150px|Mononchidae eating a Mononchidae - Wikimedia Commons]]