the “nematodes or “roundworms” (phylum nematoda) are

8/14/2019 The nematodes or roundworms (Phylum Nematoda) Are

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Nematodes

The nematodes or roundworms (Phylum

Nematoda) are the most diverse phylum

of pseudocoelomates , and one of the

most diverse of all animals.

They are very difficult to distinguish

(28,000 have been described and

undescribed roundworms might be more

than 500,000).


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HABITATThey are ubiquitous in freshwater, marine and terrestrial environments.

Found in locations as diverse in

Antarctica and oceanic trenches (90% ofall life on the seafloor of the Earth.)

Some are found in most plants and

animals (pathogens)Others undergo an ametabolic state to

respond to environmental conditions


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Systematics and

Phylogeny


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Phylum Nematoda Basal OrderMonhysterida

Basal subclass/Class Enoplia

Basal subclass/Class Dorylaimia

Class Secernentea

Subclass Diplogasteria

Subclass Rhabditia

Subclass Spiruria

Subclass Tylenchia

Chromadoria assemblage


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Physical Structures

Slender worm-like animals, typically less than 2.5mm.(smallest are microscopic, while others grow more than

5cm)

usually ornamented with rings, ridges, warts,

bristles or other distinctive structures

the mouth has 3 or 6 lips, the head is radially

symmetrical in many cases and

the rest of body is bilaterally symmetrical.

Epidermis is covered by a thick cuticle with muscles

underneath that covers the coelem


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Digestive System

The mouth often includes a hollow and sharp stylet that can beused to suck liquids from plants and animals

It has no stomach because its pharynx already

connects directly to its intestine and its wastes areexpelled through its anus. Its intestines have

valves which help control the movement of the

food in the body


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Excretory System

Nitrogenous waste is excreted in the form of ammonia through thebody walls.


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Nervous system

Four nerves run the length of the body on thedorsal, ventral, and lateral surfaces. Each lies

within a cord of connective tissue lying

beneath the cuticle and between the muscle

cells.

The ventral nerve is the largest, and has a

double structure forward of the excretory pore.

The dorsal nerve is responsible for motorcontrol, while the lateral nerves are sensory,

and the ventral combines both functions.


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At the anterior end of the animal, the nerves

branch from a dense circular nerve ring

surrounding the pharynx, and serving as thebrain.

Smaller nerves run forward from the ring to

supply the sensory organs of the head.thebody is covered with numerous number of

bristles and papillae that together provides a

sense of touch.

Behind the sensory bristles on the head lie

two small pits, oramphids.


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Amphids are well supplied with nerve

cells and are probably chemoreception

organs.


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Reproduction

Most species are dioecious, with

separate male and female individuals.

Both sexes possess one or two tubular

gonads.

In males, sperm is produced at the end

of the gonad and migrates along its

length as it mature


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The testes each open into a relatively wide

sperm duct and then into a glandular andmuscular ejaculatory duct associated with the

cloaca. In females, the ovaries each open into

an oviduct and then a glandular uterus. Theuteri both open into a common vagina, usually

located in the middle of the ventral surface.

Reproduction is usually sexual. Males are

usually smaller than females (often much

smaller)
http://en.wikipedia.org/wiki/Cloacahttp://en.wikipedia.org/wiki/Cloaca


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Nematode sperm is thought to be the only

eukaryotic cell without the globular protein G-actin.

Eggs may be embryonated or unembryonated

when passed by the female, meaning that theirfertilized eggs may not yet be developed. A few

species are known to be ovoviviparous. The eggs

are protected by an outer shell, secreted by theuterus. In free-living roundworms, the eggs hatch

into larva, which appear essentially identical to the

adults, except for an under-developed

reproductive system; in parasitic roundworms, thelife cycle is often much more complicated.


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Some nematodes, such as Heterorhabditis spp.,

undergo a process called endotokia matricida:

intrauterine birth causing maternal death.Somenematodes are hermaphroditic, and keep their

self-fertilized eggs inside the uterus until they

hatch. The juvenile nematodes will then ingest theparent nematode. This process is significantly

promoted in environments with a low or reducing

food supply.
http://en.wikipedia.org/wiki/Heterorhabditishttp://en.wikipedia.org/w/index.php?title=Endotokia_matricida&action=edit&redlink=1http://en.wikipedia.org/w/index.php?title=Endotokia_matricida&action=edit&redlink=1http://en.wikipedia.org/wiki/Heterorhabditis


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Free-living species

Usually consists of four molts of cuticle duringgrowth

Different species feed on materials as varied as

algae, fungi, small animals, fecal matter, dead

organisms and living tissues. Free-living marine

nematodes are important and abundant members

of the meiobenthos

They play an important role in the decompositionprocess, aid in recycling of nutrients in marine

environments and are sensitive to changes in the

environment caused by pollution.


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Parasitic Species

Nematodes commonly parasitic on humans

include ascarids (Ascaris), filarids, hookworms,pinworms (Enterobius) and whipworms (Trichuris

trichiura).

The species Trichinella spiralis, commonlyknown as the trichina worm, occurs in rats, pigs,

and humans, and is responsible for the disease

trichinosis.

Baylisascaris usually infests wild animals but can

be deadly to humans as well.
http://en.wikipedia.org/wiki/Trichinella_spiralishttp://en.wikipedia.org/wiki/Baylisascarishttp://en.wikipedia.org/wiki/Baylisascarishttp://en.wikipedia.org/wiki/Trichinella_spiralis


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One form of nematode is entirely dependent upon

fig wasps, which are the sole source of fig

fertilization. They prey upon the wasps, riding

them from the ripe fig of the wasp's birth to the figflower of its death, where they kill the wasp, and

their offspring await the birth of the next

generation of wasps as the fig ripens.Plant parasitic nematodes include several groups

causing severe crop losses.


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The most common genera areAphelenchoides (

foliar nematodes), Ditylenchus, Globodera (potato

cyst nematodes), etc.

Several phytoparasitic nematode species causehistological damages to roots, including the

formation of visible galls (e.g. by root-knot

nematodes), which are useful characters for theirdiagnostic in the field.

Other nematodes attack bark and forest trees. The

most important representative of this group is

Bursaphelenchus xylophilus, the pine wood

nematode, present in Asia and America and

recently discovered in Europe.
http://en.wikipedia.org/wiki/Aphelenchoideshttp://en.wikipedia.org/w/index.php?title=Foliar_nematode&action=edit&redlink=1http://en.wikipedia.org/wiki/Ditylenchushttp://en.wikipedia.org/wiki/Globoderahttp://en.wikipedia.org/wiki/Bursaphelenchus_xylophilushttp://en.wikipedia.org/wiki/Bursaphelenchus_xylophilushttp://en.wikipedia.org/wiki/Globoderahttp://en.wikipedia.org/wiki/Ditylenchushttp://en.wikipedia.org/w/index.php?title=Foliar_nematode&action=edit&redlink=1http://en.wikipedia.org/wiki/Aphelenchoides

the “nematodes or “roundworms” (phylum nematoda) are

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