Nematoda

• ecdysis - shedding of cuticle

• characteristics

  • slender

  • circular

  • triploblastic

  • pseudocoelomate

  • no blood or circulatory system

• cuticle

  • tough, thick outer layer

    • cross-linked protein chains for strength

    • collagen lattice for flexibility

  • advantage?

    • chemically and mechanically resistant

  • disadvantage?

    • they must molt the inflexible cuticle as they mature

• body cavity

  • tough cuticle = high hydrostatic pressure

    • 10x greater than earthworms

  • creates effective hydrostatic skeleton

• locomotion

  • no cilia

  • muscles rely on hydrostatic skeleton to move

  • four longitudinal sections of muscles

  • each half alternately contracts and relaxes

    • this causes lateral waves

• reproduction

  • predominantly sexual

  • sexes are usually separate (dioecious)

  • internal fertilization high internal pressure requires males to open oviduct using spicule

    • significance?

      • One of the first known intromittent organs

    • high pressure requires sperm to crawl

    • give birth to zygotes (1,000/day)

    • most of the body’s space is used for sex organs

• principle of allocation

  • as the amount of energy needed for one thing (foraging) is reduced, more energy can be allocated to other tasks

• development

  • highly unique and structured ontogeny

    • ontogeny = individual development

    • consistent sequence of cell divisions

    • fixed number of cells in each tissue and individual

      • only ~1,000 somatic cells

    • cell divisions cease early in development

      • enlargement comes from increase in cell size

    • these traits make them excellent study organisms

• ecology

  • 25,000 known species

  • highly ubiquitous

    • habitats: water, soil, plant and animal tissue

  • costly parasite of crops (root-knot nematode)

    • 5% of all crop loss worldwide

  • however, they also attack insect pests

Wuchereia bancrofti: Filariasis

• in epidemic areas, ~10% of women and 50% of men suffer

• 120 million infected worldwide

• significant gains in recent years

• cycle/stages

  • mosquito takes a blood meal

  • adults in lymphatics

  • adults produce sheathed microfilariae that migrate into lymph and blood channels

  • mosquito take a blood meal

  • microfilariae shed sheaths, penetrate mosquito’s midgut, and migrate to thoracic muscles

  • L1 larvae

  • L3 larvae

  • migrate to head and mosquito’s proboscis

Ascaris lumbricoides: Ascariasis

• 800 million humans affected

• live in small intestines

Onchocerca volvulus: Onchocerciasis (River Blindness)

• parasitized: the insect takes a blood meal from a human. A pool of blood in pumped up into the fly, saliva passes into the pool, and infective Onchocerca larvae pass from the fly into the host’s skin

• infection: the larvae enter the host’s skin tissue, where they migrate and form nodules, and slowly mature into adult worms

• proliferation: new worms form new nodules or find existing nodules and cluster together. Smaller male worms migrate between nodules to mate

• reproduction: after mating, eggs form inside the female worm and develop into microfilariae. A female may produce 1,000 microfilariae per day

• transport: when the infected host is bitten by another fly, microfilariae are transferred from the host to the fly

Dirofilaria immitis: Dog

• a mosquito bites an infected animal, ingesting heartworm microfilariae

• microfilariae mature into heartworm larvae inside mosquito (10-14 days)

• infected mosquito bites a dog, transmitting the larvae

• larvae enter the dog’s bloodstream, migrate to the heart and lungs, grow to a foot long and become sexually mature (6-7)

• adult heartworms can live within the heart and lungs for 5-7 years

• Ivermectin-resistance has developed

Trichinella spiralis: pork tapeworm

Dracunculus medinensis: Guinea worm

• 1a. human drinks unfiltered water containing copepods with L3 larvae

• 1b. infected copepods ingested by fish, frogs, or other aquatic animals

• under/uncooked fish harboring infective larvae eaten by dogs or people

• 2. larvae are released when copepods die. Larvae penetrate the host’s stomach and intestinal wall. They mature and reproduce in subcutaneous tissue

• 3. fertilized female worm migrates to surface of skin, causes a blister and discharges larvae

• female worm begins to emerge from skin one year after infection

• 4. L1 larvae released into water from the emerging female worm

• 5. L1 larvae consumed by copepod

• 6. larvae undergoes two molts in the copepod and becomes a L3 larvae