Transcript 34-1 Phylum Platyhelminthes

Phylum Nematoda & Rotifera
Section 34.2
General Characteristics:
 Bilateral symmetry
 Fluid filled body cavity





pseudocoelomate
Holds internal organs
Storage for sperm & eggs
Supports body
Structure that muscles can contract
against
Phylum Nematoda
 Roundworms
 Long, slender bodies that taper at
both ends
 1mm to 4ft
 Digestive tract with 2 openings
 Anterior – mouth
 Posterior – anus
 One directional movement
Continued…
 Most have separate sexes
 Cuticle – protective covering
 Free-living on land, salt and
freshwater
 15,000 species known
 150 species parasitic to plants and
animals
 Humans are host to 50 species!
Ascaris:
 Roundworm parasite that
lives in intestine
 Pigs, horses, & humans
 Can totally block host’s
intestine
 Up to a foot in length
 Female produces 200,000
eggs/day
Gross!
Life Cycle:
 Eggs leave with feces and enter soil
 Enter humans with contaminated
food and water
 Larvae enter intestines and
move to blood stream, then
lungs, coughed up and swallowed back
to intestines where they mate and reproduce
Hookworms:
 Another intestinal parasite
 Mouth has cutting plates that clamp
onto intestine wall
 Feed on host’s blood which may lead to
anemia
 May cause slow mental and physical
development in children
 Affects 1 billion people in tropical and
subtropical regions
Hookworm
 Enter host by boring through the feet
Life Cycle:
 Eggs leave with
feces
 Larvae develop in
soil
 Enter host’s feet
 Hitch a ride with blood to the lungs
 Coughed up and swallowed to
intestines where adult develop
Trichinella:
 Infect humans and pigs
 Adults embed in walls of intestine
 Larvae travel via blood to muscles
 Form cysts
 Humans get it from eating
undercooked pork
 Causes disease trichinosis
 Muscle pain & stiffness
 Can cause death
Other Parasitic Roundworms
1. Pinworm – most common in U.S.
 Live and mate in lower intestine
 Female crawls out at night and lays eggs
around anus
 Person scratches during sleep and
spreads eggs to everything touched
 Eggs ingested and hatch
Pinworm
2. Filarial worms – 250 million people
infected in tropics
 Found in lymphatic system (collects
excess fluid from blood vessels)
 Can cause elephantiasis
 Swollen limbs, skin hardens & thickens
 Can cause heartworm
 in dogs and cats
 Spread by mosquitoes
Elephantiasis