body units called proglottids(compartments that contain reproductive
organs). Proglottids eventually break away from the tapeworm and are
excreted in feces. However, new proglottids take their place. A tapeworm
continues to grow as long as its scolex and neck are intact.
•Taenia saginata: T. saginata, also called beef tapeworm, lives in raw or
poorly cooked beef and can cause taeniasis. T. saginatacan grow to a
length of 25 meters in the intestines of a human, leading to an intestinal
blockage and malnutrition as the tapeworm absorbs nutrients intended
for the person.
•Tania solium: T. solium, also called the pork tapeworm, lives in raw or
poorly cooked pork and can cause taeniasis. T. soliumcan grow to a
length of 7 meters in the intestines leading to an intestinal blockage and
malnutrition.- Echinococcus granulosus: E. granulosusis a tapeworm that is spread to
humans through contact with an infected dog and is transmitted when a
dog licks a person. This can lead to infection, anaphylactic shock, and
death if the tapeworm enters the body. E. granulosuscan lay eggs that
produce cysts called hydatid cystsin the lungs, liver, and brain. - Hymenolepis nana: H. nana is a tapeworm that lays eggs in cereals and
foods that are contaminated with infected parts of insects. When some-
one ingests the cereal or food he or she also ingests the tapeworm. The
tapeworm then attaches to the intestines, leading to diarrhea, abdominal
pain, and convulsions. - Diphyllobothrium latum: D. latumis a broad fish tapeworm that lives in
raw or poorly cooked fish. The tapeworm attaches to the intestines of
the fish where it then lays eggs. While attached, the tapeworm absorbs
large quantities of vitamin B 12 from the intestine eventually causing the
person to develop vitamin deficiency anemia. This is also, called perni-
cious anemiabecause there is insufficient vitamin B 12 to make red
blood cells.
ROUNDWORMS (NEMATODES)
Roundworms are also known as nematodes and live in soil, fresh water, and salt-
water. Most of the over 80,000 species of roundworms are parasites and live in
plants or animals such as insects. They have a primitive body that consists of a
cylindrical tube that has tapered ends and is covered with a thick protective layer
called a cuticle.(^180) CHAPTER 11 The Eukar yotes