1. Nematoda
Zoology 2015

2. 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

3. Phylum Nematoda It does offer adaptation potential –
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

4. Phylum Nematoda General features of this phylum –
Very diverse phylum, about 25,000 species have been catalogued but estimate that there are 500,000
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

5. Phylum Nematoda
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

6. Phylum Nematoda Form & Function of body systems – Bilateral symmetry
Complete digestive system with both a mouth and an anus

7. Phylum Nematoda Form & Function of body systems –
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

8. Phylum Nematoda Form & Function of body systems –
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.

9. 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.

10. Phylum Nematoda Form & Function of body systems –
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

11. Nematode Parasites
Ascaris lumbricoides – large intestinal roundworms of humans
More than 1.2 billion people affected worldwide
Southeastern US more than 64% of people affected

12. Nematode Parasites
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)

13. Nematode Parasites Ascaris Life Cycle
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

14. 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

15. 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

16. Nematode Parasites
Ascaris Life Cycle
Also see
Page 311
Fig. 15-7

17. Nematode Parasites Hookworm
Necator americanus – the hookworm – name means “American Killer”
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)

18. Nematode Parasites Hookworm
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.

19. Nematode Parasites Hookworm
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%.

20. Nematode Parasites
Necator americanus life cycle –

21. Colour SEM of Trichinella spiralis roundworms
Nematode Parasites
Trichinella spiralis – trichina worm
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

22. Nematode Parasites Trichinella spiralis – trichina worm (con’t)
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

23. 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.

24. Nematode Parasites Trichinella spiralis life cycle
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

25. Nematode Parasites Trichinella spiralis life cycle
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.

26. Nematode Parasites
Trichinella spiralis life cycle

27. Nematode Parasites Enterobius vermicularis – the pinworm
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

28. Nematode Parasites Enterobius vermicularis – the pinworm
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

29. Nematode Parasites Enterobius vermicularis – pinworm
Exhibit haplodiploidy
Males are haploid – come from unfertilized eggs
Females are diploid – come from fertilized eggs

30. Nematode Parasites Enterobius vermicularis – the pinworm
Diagnosed by scotch tape test or flashlight test

31. Nematode Parasites Enterobius life cycle –
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.

32. Nematode Parasites
Enterobius life cycle –

33. Nematode Parasites Filarial Worms – “Elephantiasis”
Wucheria bancrofti and Brugia malayi
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

34. Nematode Parasites Filarial Worms – “Elephantiasis”
Elephantiasis is a disease caused by repeated exposure. Blockage and swelling of lymph ducts causes gross enlargement of certain body parts

35. Nematode Parasites
Filarial Worms – “Elephantiasis”

36. Microfilarial worm infestation of eye tissue
Nematode Parasites
Filarial Worms –
River blindness - another filarial worm disease
Microfilarial worm infestation of eye tissue

37. Nematode Parasites Filarial Worms –
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.

38. Dog Heartworm Life Cycle
Nematode Parasites
Dog Heartworm Life Cycle

39. Nematode Parasites 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.