CHAPTER 18
The Ecdysozoas
Phylum Nematoda
18-1
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Nematode:
Trichinella
18-2
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Diversity

Many protostomes possess a cuticle





18-3
Non-living outer layer secreted by epidermis
Cuticle restricts growth and must be molted
via ecdysis (shedding)
Members of Ecdysozoa molt cuticle as they
grow
Regulation of molting achieved by the
hormone ecdysone
Nematodes are known as Small Ecdysozoans
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
18-4
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Diversity

Nematoda (Roundworms) are
Pseudocoelomate


Flatworms = acoelomates
Complete Guts - mouth and anus
Diversity

About 25,000 species are described


Found in virtually all habitats in all biomes


18-5
As many as half a million may exist
Topsoil may contain billions per acre
Nematode parasites exist in nearly all animal and
plant species
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Pseudocoelomate - Nematode
Ectoderm
Mesoderm
Endoderm
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Phylum Nematoda: Roundworms
Form and Function

Distinguishing Characteristics



Cylindrical shape
Nonliving cuticle
Cuticle shed during juvenile growth stages




Lack motile cilia or flagella
Longitudinal muscles in body wall
Reproduction:



18-7
Ecdysozoa
Most are dioecious with males smaller than females
Fertilization is internal
Eggs are stored in uterus until deposited
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Female Ascaris (Roundworm)
18-8
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Phylum Nematoda: Roundworms
Representative Nematode Parasites

Some are parasites of humans


Ascaris lumbricoides (Roundworm)




18-9
Most are tropical
Occurs in up to 25% of people in some areas of
the southeastern U.S.
More than 1.27 billion affected worldwide
Some species of Ascaris is found in the intestine
of horse and pigs.
A female Ascaris may lay 200,000 eggs a day,
which pass out in host’s feces
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Male and Female Ascaris Roundworm
Male is smaller (top), Female is larger
18-10
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Phylum Nematoda: Roundworms
Viable eggs remain after signs of fecal
matter have disappeared
 Survive for long periods in soil
 Host swallows embryonated eggs, juveniles
hatch, and burrow through intestinal wall
 They feed on intestinal contents and may
block or perforate the intestines
 Infection rates tend to be higher in children
and males

18-11
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Life Cycle of Ascaris Roundworm
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Phylum Nematoda: Roundworms

Hookworms





Anterior end of these small (9–11 mm) worms has a
hook-like curve
Necator americanus, most common hookworm.
Sexes are separate
Large plates in mouth cut into intestinal wall and
suck host’s blood
Pump through more blood than they digest




18-13
Heavy infections cause anemia
Eggs pass out in feces and juveniles hatch in soil
If human skin comes in contact with soil, infective
juveniles burrow through skin to blood
Travel in blood to the lungs, are coughed up to be
swallowed, and mature in the intestine
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Hookworm:
A. Mouth showing cutting plates
B. Hookworm attached to dog intestine, cutting plates pinch of intestine wall
Hookworm secretes an anticoagulant to prevent blood from clotting
18-14
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Life cycle of Hookworm
18-15
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Phylum Nematoda: Roundworms

Trichina Worm




Trichinella spiralis causes a potentially lethal
trichinosis
Adult worms burrow into intestinal wall and
females directly produce juvenile worms
Juveniles penetrate blood vessels and circulate
throughout the body to all tissues and spaces
Penetrate skeletal muscle cells



18-16
Cells lose striations and becomes a nurse cells
(continues to nourish) to the parasite
When poorly cooked meat containing encysted
juveniles is eaten, worms are liberated and mature
in the intestine
Heavy infection in mammals causes death
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Muscle infected with
Trichina worm
18-17
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Phylum Nematoda: Roundworms

Pinworms






18-18
Most common worm parasite in the U.S. but
causes little disease
Adults live in large intestine
Females, about 12 mm long, migrate to anal region
at night and lay eggs, causing itching
Scratching the anal region contaminates hands
and bedclothes
Eggs develop rapidly and become infective within
six hours at body temperature
When swallowed, hatch in duodenum and mature
in large intestine
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
A.Female pinworm from intestine
B.Group of Pinworm eggs released from anus
18-19
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Phylum Nematoda: Roundworms

Filarial Worms


Eight species of filarial nematodes infect humans
 Some cause serious diseases
Wucheria bancrofti live in lymphatic system
 Cause inflammation and blockage of the
lymphatics vessels
 Females release live young, tiny microfilariae,
into blood and lymph
 Mosquitoes ingest microfilariae when they feed
and pass to new host when they feed again
 Elephantitis is caused by repeated exposure

18-20
Swelling and growth of connective tissue causes
enormous swelling of body parts
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Life Cycle of Filarial Worm
Wuchereria bancrofti
18-21