intro 2 nematodes

8/14/2019 Intro 2 Nematodes

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NEMATODES:Form, Function, and

Classification

Eloisa D. Quizon, RMT


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General Characteristics

body elongate cylindrical

tapered at both ends

Body design is a tube within a tube

outer tube - body wall and underlying muscles inner tube - digestive tract

Pseudocoelom - fluid-filled in b/n the tubes,

reproductive system

and other structures are found;

filled with hemolymph


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General Characteristics cont.

Although there are some structural differences between

pseudocoeloms and coeloms, they confer many of the same

advantages: A space within the body cavity allows for the

reproductive and digestive systems to evolve more

complex shapes and functions

acts as a cushion, a chamber that offers protection tothe gut and other organs;

acts as a hydrostatic skeleton, providing support and

rigidity for a soft bodied animal

Sexual dimorphism is evident:

at the curved posterior end of the male there is a

copulatory organ as well as other specialized organs;

males are usually smaller than females


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Cuticlecovers the body surface of nematodes; it is

periodically moltedmetabolically active - with enzymesSpecialized structures:

-spines, bristles, warts, papillae, and ridges may be

present on the cuticle;-sensory and may aid in locomotion

not only covers the entire external surface, but it also

lines the buccal cavity, esophagus, rectum, cloaca,

vagina, and excretory pore


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Cuticle is composed of 4 Layers:

Epicuticle - thin; with a carbohydrate containing glycocalyx; acts

as a protective barrier

Exocuticle

Mesocuticle - consists of obliquely oriented, collagenous, fibrous

sublayers that vary in number and angular arrangement to each

other; they sublayers can shift their angles of orientation, thus

providing flexibility to the cuticle Endocuticle - fibrous, but

orientation of the fibers is

not distinct

A basal lamina separates

the cuticle from the

underlying hypodermis


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Hypodermis Beneath the basal lamina lies the thin, cellular (or in some cases syncitial)

hypodermis which secretes the cuticle

Protrude into the pseudocoelom along the middorsal, midventral and laterallines to form the longitiudinal hypodermal cords, partially dividing the

pseudocoel into quadrants

Hypodermal organelles such as nuclei and mitochondria are confined to the

cords

The lateral cords arethe largest and contain

the primary excretory

canal when these are

present, while thedorsal and ventral

cords contain

longitudinal nerve

trunks


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Musculature

Somatic musculature - one or more layers oflongitudinally arranged muscle cells within and

closely associated with the hypodermis

Each muscle cell comprises a contractile portioncontaining myofibrils and a non-contractile

portion in which are found the various organelles,

such as the nucleus, mitochondria, etc.

BODY WALL cuticle, hypodermis, and somaticmusculature


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Musculature cont.

An arrangement of multiple longitiudinal rows of musclecells in each quadrant is termed polymyarian, one with no

more than2 rows of cells is called holomyarian, and one

with 2 to 5 rows is meromyarian


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Digestive Tract

mouth

gut with 3

major regions

(foregut,midgut, and

hindgut);

a cloaca, &a subterminal

vent


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Digestive Tract cont.

The esophagous empties into the midgut (intestine) through a

junction called the esophago-intestinal valve

The midgut is a straight tube lined with a single layer of cells

bearing microvilli and a prominent glycocalyx

The midgut is nonmuscular, the food being moved posteriorly by

the muscular activity of the foregut and the overall bodymovements

Digestion can be intra- or extracellular or both

In females, the midgut empties into the cuticle lined hindgut or

rectum - a short, flattened tube joining the midgut and the anus In males, the posterior most portion of hindgut receives the

products of the reproductive system via the vas deferens and is

therefore called a cloaca


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Digestive Tract cont. The cuticle lined foregut begins at the mouth, which in many

species opens into a buccal capsule and continues as the

esophagus

Action of the esophagus is often enhanced by one or more

muscular enlargements called bulbs

The glandular portion of the foregut ranges from a few

unicellular glands to large prominent glands lying along the

esophagus


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Nervous System There are 2 major nerve centers in nematodes:

1. The circumesophageal commissure, or nerve ring2. The rectalcommissure

Associated with

the nerve ring are

ganglia fromwhich

longitudinal

nerves emanate

From the ventrallongitudinal nerve

is born the rectal

commissure


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Nervous System cont.

Mechanoreceptors - located around the mouth are papillae of 2

types: labial papillae on the lips surrounding the mouth and

cephalic papillae behind the lips

Other papillae may be found at different levels of the

nematode body, e.g. caudal papillae, observed in many

males; aids in copulation


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Nervous System cont.

Chemoreceptors:

Amphids are chemoreceptors located in shallow

anterior depressions or pits Phasmids are a set of chemoreceptors at the posterior end


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Excretory SystemWhen present, the basic component is comprised of 1 or 2 renettes,

large unicellular glands that empty through an excretory pore

The renettes and the excretory pore are usually locatedanteriorly

Note:

It has not been shown conclusively that this system has a function in the

removal of wastes

It may be strictly osmoregulatory


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Male Reproductive SystemOne or two testes

Vas deferens (sperm duct) extends distally to the cloaca

Two specializations of

the vas deferens are

evident before it enters

the cloaca: the seminalvesicle (sperm storage)

and the ejaculatory

duct

Sperm has no flagella

or acrosomes


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Male Reproductive System cont.

Male nematodes are usually equipped with one or more copulatory

spicules, cuticular structures are encased within spicule pouches located

laterally in the cloacal wall

The spicules are important

during copulation in that they

keep the female vulva open,

thus facilitating the entry of

sperm into the female

reproductive tract

Other accessory structure

may be present, including a

sclerotized spicular guide orgubernaculum; serves to

guide the spicules when they

are extended


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Female Reproductive System cont.

Approaching the oviduct, the oocystes detach from the rachis

and pass to a portion of the oviduct called the spermatheca,

where sperm are stored

Once fertilized, the

developing egg is moved

down the tract by a

combination of uterine

peristalsis and hydrostatticpressure

The distal portion of the

uterus, the ovijector, is

usually muscular and acts

in conjunction with the

muscles of the vulva to

expel ripe eggs


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Female Reproductive System cont.

Eggs can hatch either within the host or in the externalenvironment

Hatching of eggs in the external environment is , in

part, controlled by such ambient factors as

temperature, moisture, and oxygen tension In some species, the eggs only hatch once they have

been ingested by a host

In these cases the stimuli for hatching may be carbon

dioxide tension, pH, salts and temperature


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Molting

Nematodes undergo 4 molts each of which involves:

formation of new cuticle, loosening of the old cuticle,

rupturing of the old cuticle, and escape of the larva This sequence of events is controlled by

exsheathing fluid secreted by the larva

In some nematodes, there is a lag phase at some

stage of development, during which a phase of the

life cycle is temporarily arrested

This phenomenon is called hypobiosis

(developmental arrest) - it is thought to be anadaptation that allows the larva to withstand adverse

environmental conditions while awaiting the access

of a new host


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Larval Forms

Larval stages preceding each molt of the 4

molts in the life cycle of parasitic nematodes

are generally referred to as first-, second-, third,

and fourth-stage larvae (e.g., L1, L2 ,L3, L4) The first stage larva being the stage prior to

the first molt

However various other designations also areused for specific nematode larval forms


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Larval Forms

Rhabditiformlarva - The first

stage larva of

Strongyloides and

hookworms; theesophagus of this

small larva is joined

to a terminal

esophageal bulb by a

narrow isthmus


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Larval Forms cont.

Filariform larva - after molting twice, the rhabditiform larva of

Strongyloides and hookworms usually retain the remnants of their last

cuticle and becom ensheathed, 3rd stage or filariform larva

The esophagus is

typically elongate and

cylindrical and has noterminal bulb

This larva is usually

the stage that is

infective to thedefinitive host


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Larval Forms cont.

Microfilaria - the prelarvae of filarial worms (e.g.

Wuchereria bancrofti)

The larval body

surface is covered by

a thin layer of

flattened epidermal

cells

The primordia of

various adults

structures are visible

within the

pseudocoelom


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Phylum Nematodes:

Class Aphasmidia

(Adenophorea) Trichinella spiralis

Trichina worm

Capillaria philippinensis

Pudoc worm C. hepatica rat

Trichuris trichiura

Whipworm T. vulpis dog

whipworm


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Phylum Nematoda: Class Phasmidia

(Secernentea) Ascaris lumbricoides

Giant Intestinalroundworm A. suum Pis Ascaris

Necator americanus New world Hookworm

Anylostoma duodenale Old world hookworm

A. braziliense A. caninum A. ceylanicum


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Phylum Nematoda: C. Phasmidia(cont.)

Enterobius vermicularis

Pinworm, Seatworm

Strongyloides

stercoralis Threadworm


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Phylum Nematoda: cont.

Dracunculusmedinensis Guinea

worm, Medina worm,

serpent worm, dragon

worm Gnathostoma

spinigerum

Angiostrongylus

cantonensis Rodentlungworm

Visceral Larva Migrans Toxocara cati Cat

Ascarid

Toxocara canis Dog

Ascarid Trichostrongylus spp.

T. colubriformis

T. orientalis


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Phylum Nematoda: C.PhasmidiaFilarial Worms Blood& Tissue Nematodes Wuchereria bancrofti

Bancroft filaria

Brugia malayi Brugian

filaria

Loa loa Eyeworm

Onchocerca volvulus

Blinding worm

Mansonella perstans Mansonella streptocerca

Mansonella ozzardi


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Assignment!

In a tabulated form, enumerate all (human)

nematodes, indicate their:

Common nameStriking characteristics/ morphological feature

Infective stage

Portal of entry/ Mode of transmission

intro 2 nematodes

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