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!

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

Hookworm

Enter host by boring through the feet

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

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