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  1. Nematodes - rarity, types of hosts, classes of human parasites, unique organs
    • Nematodes are among the most abundant animals on earth
    • Free living, parasitize plants and animals
    • 2 classes...
    • secernentea (phasmidia): phasmids
    • most human-infecting nematodes
    • adenophora (aphasmidia): no phasmids
    • Phasmids: unique sensory organisms
  2. define phasmid
    • small sensory organs
    • ocated posteriorly on body surface of secernenteans (nematodes)
  3. How did parasitic nematodes likely evolve?
    • Likely evolved from soil-dwelling free-living spp
    • initially used hosts for protection or transport
    • later became physiologically dependent
  4. Describe nematodes from a historical perspective
    • Aristotle discussed Ascaris
    • Moses wrote of plague (guinea worm)
    • Ascaris/Trichuris eggs found in 2300 year-old-boy preserved in Scotland
    • Linnaeus first classified nematodes
  5. Nematodes- common name, size range, physical characteristics, reproductive characteristics
    • common name: roundworms
    • size range: <1mm to >1m (guinea worm)
    • physical characteristics: elongated
    • sharply tapered at both ends
    • round
    • bilaterally symmetrical
    • pseudocoelomate
    • body design like annelids - tube within a tube
    • outer tube - body wall and underlying muscles
    • inner tube - complete digestive system
    • triradiate lumen of pharynx
    • reproductive characteristics: dioecious with sexual dimorphism
    • females are larger w/ undeviating tail
    • males are smaller w/ curved tails
    • equiped with 1 - 2 copulatory spicules (like cirrus)
  6. Nematode - describe body wall
    • body wall comprised of cuticle, hypodermis, and muscles
    • cuticle: forms outermost covering of the body as well as the buccal cavity, pharynx, rectum, cloaca, vagina, and excretory pore
  7. Nematode - digestive system (in detail)
    • complete digestive tract w/ mouth, gut, and anus (3 regions)
    • foregut: mouth -> buccal cavity -> esophagus
    • *note- varied esophagus shapes (taxonomy)
    • midgut: AKA intestine
    • food moves w/ body movement (lack of muscle)
    • nutrient absorption/digestion
    • hindgut: anus opens to outside midventrally
  8. Nematode - describe excretory system
    • Excretion via renette cells
    • renette cells: H-shaped cells that function in excretion
  9. Nematode - describe reproductive system (in detail)
    • Dioecious (very few monecious species are known)
    • Males: 1 testis is common (2 in some)
    • sperm pathway - testis -> vas deferens -> seminal vesicle (storage) -> ejaculatory duct -> cloaca w/ 2 pouches containing copulatory spicules
    • didelphic females: 2 ovaries most common (monodelphic and polydelphic rare)
    • egg's pathway - ovary -> oviduct -> uteri -> vagina -> gonopore (vulva)
  10. Define didelphic
    • Having two ovaries (as in most nematodes)
    • see also monodelphic, polydelphic
  11. Nematode - what is unique about nematode fertilization?
    • Sperm lacks cilia/flagella and moves using pseudopods
    • migrate to upper ends of uteri where fertilization occurs
  12. Nematode - describe egg formation and anatomy
    • Feritilized eggs secrete fertilization membrane which becomes the shell
    • shell is composed of 3-4 layers (spp dependent)
    • vitelline layer: outmost layer
    • chitinous layer: most distinct of all layers
    • lipid layer (AKA vitelline membrane): responsible for impermeability
    • proteinous layer: outermost layer for some, can be smooth (Trichuris) or rough (Ascaris)
    • *NOTE - eggs vary considerably in size and appearance
  13. Nematode - describe egg hatching and growth
    • *significant variation
    • Can hatch inside or outside host
    • Some hatch only when swallowed by suitable host (internal conditions stimulate larva to hatch)
    • grow by molting (like arthropod)
    • molting: formation of new cuticle -> loosening of old cuticle -> breakage of old cuticle -> escape of cuticle
    • *undergoes 4 molts
    • hypobiosis: in some, lag phase at some stage of development
  14. define hypobiosis
    • occurs in some nematodes
    • developmental arrest that causes a lag phase at some stage of development
    • Allows survival in unfavorable condition
  15. Nematode - larval form information (in detail) w/ specific, named stages
    • Nematodes undergo 4 molts (L1, L2, L3, L4)
    • *NOTE- these are not the same stages for each nematode
    • rhabditiform: first-stage larvae of hookworms
    • posterior esophagus has prominent bulb, separated from anterior portion by thin isthmus
    • filariform: after molting twice, rhabditiform larva become ensheathed to form L3 
    • esophagus is extended and cylindrical without bulb
    • *NOTE- this is infective stage for definitive hosts
    • microfilaria: juvenile, first-stage larva of filarial nematodes (Wucheria bancrofti, Loa loa)
    • body covered in thin, cuticular sheath
    • first signs of various structures are visible
    • *NOTE - found in circulating blood and cutaneous tissues (microscopic)
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2014-12-16 00:48:08
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