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Unit 5 Review #4
Round worms belong to Phylum NEMATODA
Most round worms are actually free-living, but
we focused on the parasitic ones.
An acoelomate is an animal that does not possess
any true body cavity. A coelomate is an animal
that is completely lined by mesodermally-derived
tissues. In contrast, a pseudocoloem is lined to
the outside by mesoderm and a bit of ectoderm
tissue and the inside is from endoderm. See
Roundworms possess a PSEUDOCOELOM
The majority of roundworms are dioecious.
Therefore they must find the opposite sex to
complete sexual reproduction.
Complete guts have a mouth at one end an anus
at the other. Incomplete guts use the mouth to
take in food and expel wastes. The advantage is
that a complete gut does not mix waste with
food, it is much more efficient. Round worms use
a complete gut, that is one of their advancements.
Both Annelids (segmented worms) and
Nematodes (round worms) use bilateral
symmetry. So did Platyhelminthes (flat worms)
Possessing a Coelom or even a Pseudocoelom
provides the adavantage of creating space for
separate organs to sit and work without
interfering with other tissues and organs.
Example, the circulatory system can work
without interfering with movement in the
digestive system.
See the picture below:
DORSAL Surface
Anterior End
10. The most common parasitic round worm in
Canada and U.S. is the "pinworm".
11. A) GUINEA worm
B) Filarial lymphosis causing Elephantiasis.
C) Ascaris
D) Heartworm
E) Trichinella
F) River blindness roundworm- A filarial worm
called "Onchocerciasis".
12. A) Hookworm
B) Ascaris
C) Pinworm
D) Elephantiasis – A type of filarial worm
12. Segmentation : Is the repetition of units that
bear similar patterns of muscle and nervous
structures as well as other organs.
13. Three classes of ANNELIDA include: POLYCHAETA,
14. Leaches belong to class Hirudinea, leaches
posses a) Suckers, b) Anticoagulant and c)
15. Marine worms belong to class POLYCHAETA.
16. Earthworms belong to class OLIGOCHAETA.
17. Earthworm digestive (MPECGI) tracts include: a)
Pharynx for sucking in food and passing onto
Esophagus. B) Crop which stores food
temporarily C) Muscular Gizzard for grinding up
food. D) Intestine for absorbing nutrients into
blood stream.
18. Digestive Gland cells produce enzymes for
19. Peristalsis is a rhythmic contraction of circular
and longitudinal muscles that pushes things along
inside the digestive tract.
20. Earthworms posses a closed circulatory system,
in larger animals this system delivers blood to
tissues much faster and more efficiently than in
an open circulatory system.
21. Setae are bristles that the worm can extend and
retract, these bristles can help provide traction
and can be used for anchoring it into its burrow.
22. Hemoglobin is the protein molecule that carries
O2 and makes blood red.
23. There are 5 pairs of hearts. So a total of 10
24. The Belly surface is VENTRAL the rear region is
25. The Back surface is DORSAL and the front region
26. Earthworms keep skin moist and protected with
outer cuticle and mucous glands.
27. The simple brain is located just dorsal to the
28. The brain branches off to form two
circumpharyngeal nerves that go around the
pharynx and then merge together to give rise to
the ventral nerve cord.
29. Both motor nerves and sensory nerve attach
onto the ventral nerve cord.
30. Hermaphrodites are individuals that posses both
male and female reproductive organs.
31. Testes would be located in segment 10 and 11.
They are responsible for Sperm production.
32. Ovaries are located in segment 13 and they
produce eggs.
33. The clitellum is a swollen ring that contains a
great number of mucous gland cells these
secretions play an important role in mating and
in protecting the developing embryos.
Evolutionary Advancements
Nematodes have a Pseudocoelom and their
digestive tract is a complete gut.
Most Nematodes are dioecious (separate
sexes) this ensures for better genetic
diversity as they must find a mate for sexual
Dioecious – Separate sexes. Monoecious –
Annelids are more advance than nematodes
in that they possess a True Coelom, a closed
circulatory system and a much more
advanced digestive tract.
In Nematodes a fluid filled pseudocoelom
circulates oxygen and nutrients and picks up
metabolic wastes. In Annelida blood
circulates through hearts and blood vessels.
Disorders Caused by Parasitic Roundworms:
Guinea worms are transmitted through
contaminated drinking water that contains
infected copepods (small crustacean). The larvae
hatch out and reach sexual maturity in the
human intestine. The worms mate and the males
die. Females then migrate from gut into body
tissue and grow up to a meter in length just
under the skin. Then they form an ulcer through
the skin to release their fertilized eggs back into
the water.
Filarial worms block lymphatic
vessels. These larvae are transmitted through biting
insects (especially mosquitoes). They then circulate
around lymph vessels, they grow and reproduce
sexually. As they grow they often block the lymph
vessels (especially those vessels of the arms, legs,
scrotum and breasts) causing enormous swelling and
inflammation. Then a biting insect bites host to pick
up microfilarial larvae and transmit to another host.
The main disorder associated with hookworms is
PARASITIC ANEMIA. As hookworms anchor into
gut they feed off of blood in the tissues leaving
the host low on blood and more prone to other
4.About 25 % of the world’s population are afflicted
with hookworms. Juvenile hookworms developing in
soil, then burrow into host through the skin. Then they
circulate through the blood stream and reach the
intestinal wall where they anchor and suck blood and
tissue fluids. They reach maturity and sexually
reproduce to release fertilized eggs into feces.
5 – Trichinella spirellis is a small (3-4 mm) roundworm
that lives in the intestine of its host and causes little
problem during this stage of its cycle. When they
sexually reproduce the female holds the fertilized eggs
in her body and then give birth to hatched larvae.
These larvae burrow through the intestinal wall and get
into the blood or lymph systems. They then burrow into
organs and muscles causing excruciating pain/fevers etc.
They then encyst themselves and lie dormant. When
these tissues are consumed by another animal they
hatch out and reach sexual maturity in the intestinal