Phylum Nematoda & Rotifera Section 34.2
Jan 03, 2016
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
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
Life Cycle:
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
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
Life Cycle:
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
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