Nematoda
ZOOLOGY
2015
PHYLUM NEMATODA

Adaptive Benefits of a
Pseudocoelom - a space
between the guts and the
body wall
It is not lined with a
peritoneum therefore is
termed a false cavity
 It is an improvement over
the acoelom of the
platyhelminthes but not as
advanced as the eucoelom
/ it lacks mesenteries

PHYLUM NEMATODA

It does offer adaptation potential –
1.
2.
3.
4.
5.
Greater freedom of movement
Space for development and differentiation of
digestive, excretory and reproductive organs
Storage for waste products
Simple means for distribution and circulation of
materials
Hydrostatic support for the body
PHYLUM NEMATODA

General features of this
phylum –
1.
Very diverse phylum,
about 25,000 species
have been catalogued but
estimate that there are
500,000
a)
2.
In good topsoil there are
billions per acre of ground.
They live in all habitats,
from mountains to the
deep oceans, from the
polar ice to the tropics
PHYLUM NEMATODA
3.
4.
5.
6.
Free-living nematodes feed on yeast, bacteria
and algae
Predatory nematodes feed on other invertebrates
and protozoans
Nematode worms are important food for mites,
insects and fungi
Almost all animals and most plant species have
nematode parasites
PHYLUM NEMATODA

Form & Function of body systems –
A.
B.
Bilateral symmetry
Complete digestive system with both a mouth
and an anus
PHYLUM NEMATODA

Form & Function of body systems –
C.
D.
E.
Nematodes all have a cylindrical shape
Muscles in body wall only run longitudinally
Nematodes express Eutely which means they all
show a set number of cells

Examples – C. elegans



Researchers use this worm
Females have 1057 cells
Males have 959 cells
PHYLUM NEMATODA

Form & Function of body systems –
F.
F.
Dorsal and ventral cords bear nerves while lateral cords
bear excretory ducts
Longitudinal muscles
run in four bands –
between the nerve
and excretory cords
The digestive system
consists of mouth,
pharnyx, intestine,
rectum and anus.
This is considered a complete digestive system.
PHYLUM NEMATODA

Form & Function of body systems –
Senses include papillae (sensory hairs) at the head and
tail and amphids on the head. Parasitic
nematodes also have phasmids (chemo-receptors)
at the tail end
Nematodes are dioecious
and the males are smaller
than the females and
fertilization is internal.
Males bear a pair of copulatory spicules.
PHYLUM NEMATODA

Form & Function of body systems –
K.
L.
Nematodes have a non-cellular cuticle that is
shed between each of four juvenile stages (no
larval stage) this is called molting
Skeletal system is hydrostatic
NEMATODE PARASITES

Ascaris lumbricoides –
large intestinal
roundworms of humans
A.
B.
More than 1.2 billion
people affected
worldwide
Southeastern US more
than 64% of people
affected
NEMATODE PARASITES
C.
D.
They feed on intestinal
contents and a large
infestation may block or
perforate the intestines.
They may cause a serious
anemia in children
Females may be 50 cm –
20 inches) long and males
30 cm - (12 inches)
NEMATODE PARASITES

Ascaris Life Cycle
1.
2.
3.
A female roundworm lays 200,000 eggs a day
which pass out in the host’s feces
Eggs remain viable for long periods in the soil –
(10-20 years)
When a host swallows the eggs, juveniles hatch
and burrow through intestinal wall into the blood
supply
NEMATODE PARASITES

Ascaris Life Cycle (con’t)
4. Carried through the heart to the lungs, they break
into the alveoli and crawl upward into the trachea
where they are coughed up and then swallowed
with saliva
NEMATODE PARASITES

Ascaris Life Cycle (con’t)
5. They mature in the intestine
where they feed on the
intestinal contents. They
sometimes cause allergic
reactions or perforation of the
intestine which results in
peritonitis. Wandering worms
may occasionally emerge from
the throat or anus and have
even been known to appear
wriggling out of the ears,
mouth or nose if there is a
heavy infestation
NEMATODE PARASITES

Ascaris Life Cycle
Also see
Page 311
Fig. 15-7
NEMATODE PARASITES

Hookworm

Necator americanus – the
hookworm – name means
“American Killer”
A.
B.
These are small worms, only 11 mm
and their anterior end has a dorsal
curving hook (male)
Large sharp cutting plates in their
mouth cut into the intestinal mucosa
and they attach and suck the host’s
blood (see page 310, figure 15-6)
NEMATODE PARASITES

Hookworm
C.
D.
Hookworms become blood pumps because they
pump much more blood than they can digest,
pumping the blood through their intestines,
partially digesting it and absorbing the nutrients.
They suck much more blood than they need for
food and heavy infestations can cause anemia.
Children with hookworms may experience retarded
mental and physical growth.
NEMATODE PARASITES

Hookworm

1.
2.
Necator life cycle –similar to that of the Ascaris
Eggs pass in feces, but if soil conditions are warm and
moist the eggs hatch and the juveniles live in the soil,
eating bacteria.
When juvenile worms come into contact with bare skin,
they burrow into the blood vessels and then they follow
the same path as Ascaris to get to the intestine.
Penetration usually occurs through soles of the feet.
Southern US population had a 55% infection rate at
the turn of the century but because of the practice of
wearing shoes the infection rate is now 5-10%.
NEMATODE PARASITES

Necator americanus life cycle –
NEMATODE PARASITES

Trichinella spiralis –
trichina worm
A.
B.
C.
Causes the potentially
lethal disease
trichinosis
About 2.4% of the US
population is infected
Adult worms are tiny,
about 1.5 – 3 mm
long
Colour SEM of Trichinella spiralis
roundworms
NEMATODE PARASITES

Trichinella spiralis –
trichina worm (con’t)
D.
Infection occurs when
meat containing live
encysted juveniles is
eaten, adults burrow
into intestinal mucosa
and females give birth
to live young
Muscle tissue with encysted larval trichina
NEMATODE PARASITES

Trichinella spiralis – trichina worm (con’t)
E. Trichina worms infect hogs, rats, cats, and dogs . . .
People usually become infected by eating undercooked
pork.

Hogs become infected by eating infected meat scraps or
infected rats.
NEMATODE PARASITES

Trichinella spiralis life cycle
1.
2.
In an infected host, living juvenile worms
are born in the intestine
Juveniles penetrate blood vessels and
circulate through the body invading all
organs, tissues and intestinal spaces
NEMATODE PARASITES

Trichinella spiralis life cycle
3.
4.
When they invade skeletal muscles, they
redirect genes and muscle looses its striations
and becomes a nurse cell of the parasite. This
this encysted meat is eaten, it cause the
infection.
While the juveniles are wandering in the body,
they can cause death if large numbers invade
the heart or the brain.
NEMATODE PARASITES

Trichinella spiralis life cycle
NEMATODE PARASITES

Enterobius vermicularis –
the pinworm
A.
B.
C.
This is the most common
worm parasite in the US but
it causes little disease (just
irritation)
Adults live in the large
intestine
They attain a body length of
12 mm
NEMATODE PARASITES

Enterobius vermicularis – the pinworm
D.
E.
F.
30% of US children are infected
Up to 75% of college students who live in dorms
are infected
There are several oral drugs that are effective
against this infection but all people living in the
household must be treated because they are very
infectious
NEMATODE PARASITES

Enterobius vermicularis
– pinworm
G.
Exhibit haplodiploidy


Males are haploid –
come from unfertilized
eggs
Females are diploid –
come from fertilized
eggs
NEMATODE PARASITES

Enterobius
vermicularis – the
pinworm
H.
Diagnosed by
scotch tape test
or flashlight test
NEMATODE PARASITES

Enterobius life cycle –
1.
2.
3.
4.
5.
Adults live off of intestinal contents in the large
intestine
Females detach from the intestinal lining and migrate
to the anus at night to lay eggs on the external
surface. This causes intense itching.
Scratching the itch contaminates hands and bed
clothes
Eggs develop rapidly and can become infective in just
6 hours at body temperature
Contaminated hands put eggs into mouth and
airborne –eggs hatch in the duodenum and mature in
the large intestines.
NEMATODE PARASITES

Enterobius life cycle –
NEMATODE PARASITES

Filarial Worms – “Elephantiasis”

Wucheria bancrofti and Brugia malayi
A.
B.
C.
D.
250 million people in the tropics are infected
Worms live in the lymph system and obstruct the ducts
Worms may grow to 100 mm
Females release live young called microfilariae which
circulate in the blood stream
Brugia malayi
Wucheria bancrofti
NEMATODE PARASITES

E.
Filarial Worms – “Elephantiasis”
Elephantiasis is a disease caused by repeated
exposure. Blockage and swelling of lymph
ducts causes gross enlargement of certain
body parts
NEMATODE PARASITES

Filarial Worms – “Elephantiasis”
NEMATODE PARASITES

Filarial Worms –
D.
River blindness - another filarial worm disease
Microfilarial worm
infestation of eye tissue
NEMATODE PARASITES

Filarial Worms –
E.
Dog heartworm is the most common filarial worm
disease in the US. It reaches a 60% infection rate
in the south and eastern seaboard states and can
infect dogs, cats, otters and occasionally humans.
NEMATODE PARASITES
Dog Heartworm Life Cycle
NEMATODE PARASITES

1.
2.
3.
4.
5.
Filarial Worms Life Cycle –
Adult worms live in the lymph ducts
Females bear live tiny juveniles called microfilariae
At night, microfilariae congregate in vessels near the
surface of skin
Mosquitoes transmit disease when they ingest the
microfilariae as they feed
The microfilariae develop into the infective stage in
the mosquito, considered the intermediate host and
then they infect a new definitive host by moving into
a bite wound through the proboscis of the mosquito.