Biology 625
Fall semester lecture note outline

Updated: 01 September 2005

The text below simply represents a crude lecture outline of one of the topics covered in class. It is not meant to substitute for attending lectures or ignoring the textbook. Additional material, including line drawings, kodachromes, and more extensive information on life-cycles and basic biology, will be supplied in the lectures.

Topic #24. The Phylum: Nematomorpha

  1. Common names include horse-hair worms, hair worms, or gordiacean worms
  2. Long, slender, worms sometimes up to a meter in length and up to 3 mm in diameter
  3. Resemble nematodes superficially, but in a separate phylum
  4. Sexes separate (dioecious)
  5. Common hosts include beetles, crickets, grasshoppers, cockroaches, millipedes, centipedes, etc.
  6. Pseudocoelom; filled with mesenchymal cells
  7. In adults, digestive tract degenerate both anteriorly and posteriorly; food absorbed across the tegument
  8. No excretory system
  9. Males usually with tail ventrally coiled
  10. Yellowish to dark brown in color
  11. Characteristics that help distinguish this phylum from Mermithids
    1. Body does not taper at both ends (unlike nematodes); ends more blunt and rounded
    2. Anterior portion of the body termed a calotte, and set off from the rest of the body by a pigmented, circular collar
  12. Covered by thin layer of cuticle
  13. Posterior portion of body often split into 2 (males) or 3 (females) lobes (although not all species are split posteriorly)
  14. Cuticle often rough, due to round/polygonal cuticular plates, the areoles; may be more than one type of plate on cuticle; some with intrareolar bristles, pores, or papillae
  15. Most in the class: Gordioidea and are tied to fresh water
  16. About 17 species are currently recognized as valid in North America (2003, Proc Acad Nat Sci Phil 153: 77-117).
  17. Common species in the US
    1. Paragordius varius (Family: Chordodidae)
      1. male posterior end bi-lobed with elongate lobes, each lobe about 2.5 to 3 times as long as wide; no crescent-shaped fold in postcloacal region
      2. female posterior end with 2 elongate lobes
      3. one type of areole (fairly distinct); without intrareolar bristles
    2. Gordius robustus (Family: Gordiidae)
      1. male posterior end bi-lobed with blunt lobes, each lobe about twice as long as wide; distinct crescent-shaped fold in postcloacal region
      2. female posterior end without lobes
      3. one type of areole (somewhat indistinct) ; some intrareolar bristles
  18. Life-cycles
    1. Female lays large number of eggs; sometimes one million or more in strings in water or moist soil; female dies in Fall after egg laying
    2. Larvae develop; each with an armed proboscis
    3. Exit egg
    4. Some nematomorphs can probably develop directly in some hosts, and also use interemediate hosts in some scenarios.
    5. In a direct life-cycle, some species bore directly into an arthropod; other species encyst and wait to be eaten by arthropod, then excyst in gut.
      1. Cross gut wall
      2. Often migrate to body cavity or fat bodies
      3. Develop into subadult (most castrate host in process)
    6. Recent studies have shown that intermediate hosts can also be involved, at least for some species (1999, J Parasitol 85: 139-141).
      1. Larvae of Gordius robustus ingested by aquatic arthropods; encyst in posterior portion of midgut wall.
      2. Insect undergoes metamorphosis and moves onto land, where it is preyed upon or scavenged by cricket
      3. Cysts ingested by crickets (i.e., eat viscera of dead intermediate host)
      4. Worm crosses gut wall
      5. Matures in hemocoel
      6. This is likely to be method that some terrestrial arthropods become infected; i.e. by ingestion of tissues from aquatic intermediate host harboring encysted larvae.
    7. When insect contacts water, worm emerges; host usually dies but in some cases may live several months.
    8. These elongate worms are often seen in creeks and ponds, free in environment after a rain, in pet water bowls or toilet bowls (usually with a deceased arthropod nearby)
    9. Male and female worms coil, then copulate in water

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