Download free-living worms

27-2 Roundworms : Phylum Nematoda
includes free-living worms and parasitic worms that cause disease
ex) hookworm, filarial worm, trichinosis
Roundworms are unsegmented worms that have a digestive system with two
openings.
Three germ layers with a cavity that is partially lined with mesoderm.
This forms the pseudocoloem: a partial body cavity that allows them to
have a mouth and anus (pseudo=false)
Feeding
Many free-living roundworms use grasping mouthparts and spines to catch
prey. (Predators) Some eat algae and decaying matter. Others are parasites.
Respiration, Circulation, and Excretion
Use gas exchange through thin body walls. Use diffusion to get oxygen to
cells and eliminate waste
Response
Have simple nervous systems consisting of several ganglia (group of
neurons). Nerves extend from head along sides of body. Nerves transmit
information and control movement.
Movement
The muscles of roundworms work with the fluid in the pseudocoleom as a
hydrostatic skeleton, similar to a jellyfish. They move in a snakelike fashion
through water, or push their way through soil by thrashing.
Reproduction
Roundworms reproduce sexually. Many have separate sexes—either male
or female. A male deposits sperm inside the females reproductive tract.
Roundworms and Human Disease
Phylum Nematoda although most species are free-living, this phylum is
better known for its parasitic members
Trichinosis-causing worms
Trichinosis is a disease caused by the roundworm Trichinella. Adult worms
live and mate in the intestine of their host. The female worm carrying the
fertilized eggs burrows through the intestine wall and releases larvae into the
bloodstream. The larvae form inactive cysts in the muscles and organs of the host.
Trichenella completes its life cycle when another animal eats the muscle tissue of
the infected host. Two common hosts are rats and pigs. Humans get Trichinosis
when they eat cyst infected muscle of undercooked pork.
Filarial Worms
Common in Asia, filarial worms are threadlike worms that live in the blood
and lymph vessels of birds and mammals. They are transmitted by mosquitos who
ingest larvae from an infected hosts bloodstream. In severe infections the blood
flow is blocked by the worms, causing a disease otherwise known as Elephantiasis
an untreated case of Elephantiasis
Ascarid Worms
Ascaris lumbricoides is a parasite that causes malnutrition in more than 1
billion people worldwide. It absorbs digested food from the host’s small intestine.
It can lead to death if allowed to block the intestine. Fertilized eggs are released
into the host’s feces. In countries with sewage problems, food and water sources
are contaminated with infected feces. If eaten by a healthy person, they will be
infected with Ascaris.
There are other animals that are infected with other species of Ascarid worms
similar to Ascaris lumbricoides, such as dogs, cats, chickens, pigs and horses. The
reason puppies and kittens are wormed at young ages is to rid them of Ascaris.
Ascarid worms blocking
the small intestine of a hen
Intestinal worms
in humans cause
malnutrition
and a distended
abdomen
Hookworms
As many as 25% of the world’s population is infected with hookworm.
Hookworm eggs hatch outside the body and develop in the soil. They infect their
host by using sharp tooth-like hooks to burrow into the skin and enter the
bloodstream. They suck the host’s blood and cause weakness and poor growth.
Hookworms can be passed by exposure to fecal matter, or soil that has been near
fecal matter of an infected host. They can pass between dogs, cats and humans.
Mouth of a hookworm under
magnification
Tissue damage due to
hookworm infection
after it burrowed
through the skin 