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Phylum Nematoda
Examples
Roundworms◦ Dioctophyma renale – Inhabit the kidney, very large.
Examples
Roundworms◦ Ancylostoma duodenale – Also known as Hookworms, these live in
the small intestine and feed off of the blood.
Examples
Roundworms◦ Trichinella spiralis – Cause trichinosis, found in pigs and other
animals such as bears.
Examples
Roundworms◦ Ascaris lumbricoides – The most common of the roundworms, as
they infect as many as 1 billion people worldwide.
Introduction
Phylum Nematoda
◦ Many are microscopic parasites, but some
species can reach extraordinary lengths –
sometimes over 1 m
◦ Very abundant – widespread throughout the
world
◦ Consists of over 90,000 species
◦ Free-living and parasitic species
Free living species are important in the ecology of
soil -> they function as decomposers
Features
◦ “round” worms
◦ Free-living or parasitic
◦ Bilateral symmetry
◦ Cephalization, -- but not very well-defined
◦ Tissues formed from 3 true cell layers in embryo
Ectoderm, mesoderm, endoderm
◦ Unsegmented
◦ Internal organs found in the pseudocoelom
◦ Digestive tract with 2 openings (tube within a tube)
◦ Mouth and anus
◦ Body is covered with a thick cuticle
Body Plan
Pseudocolem
Body Structure
Response
Simple nervous system
Ganglia
Sense organs
No respiratory system
◦ Diffusion oxygen in, carbon dioxide out
No circulatory system
◦ Nutrients diffuse through internal tissues
No excretory system
◦ Wastes diffuse through internal tissues
Across body wall
Respiration, Circulation and Excretion
Feeding
Parasitic worms
◦ attach to their host
Free living
◦ use grasping mouthparts to catch and eat
smaller animals
◦ Algae or bacteria
Digestive System
Simple digestive system containing a mouth
leading to a short, muscular pharynx that the
nematode uses to suck in food.
The intestine is made of one layer of cells for
absorption of food. The parasitic nematode
intestines do not contain any digestive gland
cells to create enzyme to breakdown food.
Why?
At the end of the intestine, it opens up to the
anus near the posterior tip for excretion of
unabsorbed food.
Digestive System
Nervous System
Simple
Consists of a ring of nervous tissue around the pharynx
called Nerve Ganglion (simple brain) AND nerve tissue
running down the length of the nematode on the dorsal
and ventral trunk.
Reproductive System
Sexes are separate – males are usually smaller
than females
Each consists of a long tube (single in a male,
paired in a female) – which coils back and forth in
the body space
Reproductive System
Female Reproductive System
Paired long tube coils back and forth
in the body space
The two ovaries are long and slender
and widens into two large tubes (the
uterus) where the eggs accumulate.
The uteruses unite into one short
duct (the vagina)
Male Reproductive System
The male’s testis consist of a long
coiled tube were the sperm are
formed.
It gradually enlarges into the
sperm duct, which opens near the
posterior end.
The sperm is transferred to the
female with the aid of a pair of
bristles.
Parasitic Round Worms
Ascaris
One of the most common intestinal
parasites in humans -- over 1 billion
people have it
Lives in small intestine but travels through
the body as a juvenile
Ascaris
Hookworm (Ancylostoma) Hookworm
Human hookworm (Necator sp.) feeds on blood
from inside of intestine
A single worm can drain 20 ml of blood per day
Most serious in children as can lead to physical
and mental retardation
Enters as “Itch worm” between toes
Pinworm (Enterobius)
Lives in lower bowel
Female migrates out anus each night to lay eggs
Secretes irritating toxin to get person to scratch
Re-infection is oral
Trichinella
A serious infection that humans can
contract when eating rare pork containing
encystedTrichinella larvae
Invades selected muscles forming painful
cysts
Causes Trichanosis
Trichinella
Filarial Worms
Is a parasite of dogs
Live in the heart and arteries
Filarial Worms
In humans, the filarial worm causes
elephantiasis
Restricted to the tropical areas of Africa
Uses mosquitos as a secondary host
Adult worms reside in the lymph vessels
which impedes the movement of fluids
causing swelling
Elephantiasis
Guinea Stick Worm
(Dracunculus) In Africa only
Enters while a person is in contaminated
water and burrows through skin and
grows
No cure - is removed by wrapping around
a stick - one turn per day
Contains deadly toxin if broken it can kill
its victim
New Guinea worm