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Roundworms
Brittney Jackson, Kaylee Kraft,
Jessica Lin
Basic Information
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Phylum Nematoda
Key roles in decomposition and nutrient recycling
Habitat: soil, marine, freshwater sediment
More than 15,000 species
Most are free living
Parasites in animals and plants
Roundworm Bodies
• Microscopic bodies
• Movements produced by contraction of longitudinal muscles
• Elongated, cylindrical, threadlike body which is pointed at
both ends and covered by a tough, flexible cuticle
• Cuticle gives nematode body shape and protection
• Epidermis not composed of distinct cells
• Beneath epidermis is a layer of longitudinal muscles
• No circular muscles present in the body wall
• Fluid filled pseudocoelom (fluid filled cavity that contains
transports nutrients) that serves as a hydrostatic skeleton
• Bilateral symmetry, complete digestive tract, complete
digestive tract, three definite tissue layers, and definite
organ systems
Roundworm Bodies Continued
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Lack specific circulatory structures
Sexes are usually seperate
Male is smaller than the female
Absence of a well-defined head
Gas Exchange/ secretion
• no circulatory system
• gas exchange and secretion by diffusion
Response to Stimuli
• Sensory Organs
o sensory hairs and papillae over the entire body
o Amphids- located on the head; small cavities; function as chemical
receptors
• Nervous System
o 4 main nerves
 entire length of the body
o dorsal nerve
 controls muscle movement
o lateral nerves
 sensory information
o ventral nerve
 motor skills
• Brain
o rings of the four primary nerves
o motor responses
o move to or away from stimuli
Movement
• thrash around
• coil and uncoil
• movement produced by the longitudinal muscles
Classification and Evolution
• Traditionally classified as a single phylum based on
wormlike body strucutre
• Molecular evidence suggests roundworms evolved from
complex animals by a simplification of their bodies
• Probably related to arthropods and can be classified as
Ecdysozoa since like other arthropods/ecdysozoans they
shed their cuticles periodically
Diseases
• Ascariasis
o Symptoms: coughing, shortness of breath, weight loss, nausea, blood in
stool, worms in stool
o Cause: contaminated food/water, Ascaris ( white worm)
• Guinea worm disease
o Symptoms: start a year after infection when the worm is ready to lay eggs,
which emerges through the skin producing a painful blister
o Cause: contaminated water
• Loiasis
o Symptoms: itchy eyes, blurred vision, people see worms move across
their eyes
o Cause: Loa loa transmitted by day-biting flies
• Lymphatic filariasis
o Symptoms: swelling/scarring of the legs/groin
o Cause: mosquito bites
• River blindness
o Symptoms: itchy rash, lose skin pigment, lose vision
o Cause: spread by day-biting flies, leading cause of worldwide blindnes
Diseases Continued
• Trichinosis
o Symptoms: diarrhea, high fever, muscle pain, sensitivity
to light, headache, and pink eye
o Cause: eating uncooked meat
• Threadworm
o Symptoms: nausea, diarrhea, fever, coughing up blood,
Ascariasis
Guinea worm disease
Lymphatic filariasis
Ascaris
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10 inches long
adult life in human intestine
separate sexes
female can produce up to 200,000 eggs a day
o leave human body with feces
 human waste as fertilizer, encourages the parasite
1. eggs hatch in the intestine
2. larvae burrow through the intestinal wall into blood or lymph
vessels
3. carried through the heart and lungs (cause damage)
4. eventually go back to the small intestine where they settle
and mature
Hookworm
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less than 1.5 cm
live in the human intestine
larvae hatch and feed on bacteria in the soil
host walks barefoot; microscopic larvae burrow into the skin;
then enter the bloodstream
• move to the intestine for maturation
• hook onto the lining of the intestine and suck the blood
Trichina Worm
• can live in pigs, rats, and bears
• infection occurs in humans by eating raw or undercooked
meat
• live in the small intestine
• larvae migrate to the skeletal muscle and encyst
• in order to survive the host needs to be eaten
o if not, the larvae are not freed from their cysts and
eventually die
• cysts are calcified and remain in the muscles
o cause stiffness
Pinworms
• found commonly in children
• ingested by eating with hands contaminated with the small
eggs
• live in the large intestine
• female worms move to the anal region to deposit the eggs
o causes itchiness
• the eggs may be distributed through the air and therefore
around the house
Reproduction
• sexual
• Female: ovary, oviduct, uterus (fertilized
here)
• Male:sperm cells made in the testis, sperm
cells pass through the spicule
• eggs deposited into the soil after fertilization