1. Phylum Nematoda (Nemata)
  2. Diversity
  3. Phylogeny (briefly)
  4. Bauplan Basics
  5. Feeding
  6. Circulation/Gas Exchange
  7. Osmoregulation/Excretion
  8. Nervous System
  9. Movement
  10. Reproduction

  1. Diversity
  2. More individual nematodes than members of any other phyla?
  3. Free-living forms found in nearly every environment
  4. Free-living marine & freshwater
  5. Between grains of beach sand
  6. Key soil dwellers (nutrient processing)
  7. Polar ice fields
  8. Key plant & animal parasites
  9. Phylogeny
  10. Hypothesis 1: Based on body plan and development
  11. Detour: Other Blastocoelomates
  12. Hypothesis 2: Based on molecular evidence and other aspects
  13. Bauplan Basics
  14. Protostome features include
  15. Triploblastic (distinct mesoderm  muscles)
  16. Bilateral symmetry & cephalization
  17. Cell fate is determinate
  18. No spiral cleavage
  19. Cleavage pattern unique to Nematoda
  20. Blastocoel forms blastocoelom (=pseudocoelom)
  21. Feature shared by several phyla
  22. Cuticle
  23. In common with Arthropod cuticle:

a)Contains chitin

b)Secreted by epidermis

c)Several layers

d)Molts with growth

Ecdysone is key hormone

  1. Fibers form flexible coil  elastic qualities for movement
  2. Varies in appearance
  1. Feeding/Digestion
  2. Simple mouth, or with stylet, teeth, jaws, etc…
  3. Muscular pharynx (a.k.a. esophagus) lined with cuticle
  4. Use of suction
  5. Digestive system usually simple, not highly branched
  6. Intestinal microvilli increase surface area
  7. Some with bacterial symbionts & reduced digestive system
  8. Gas exchange
  9. Body surface
  10. Pseudocoelomic (=blastocoelomic) cavity
  11. Exchange between pseudocoelomic (=blastocoelomic) fluid and organs
  12. No circulatory system
  13. Osmoregulation/excretion
  14. System of lateral cords connected to a large cell ("renette")
  15. Associated with digestive system
  16. Not well-studied
  17. Empties via excretory pore
  18. Excretion also via the digestive system
  19. Nervous system
  20. Organization
  21. Nerve ring

a)Plus associated ganglia

b)Sensory nerve input (from head)

  1. Four major nerve cords: 1 dorsal, 1 ventral, 2 lateral

a)Ventral cord may be fused & with ganglia (as in Annelida and Arthropoda)

  1. Connection of longitudinal muscles is unique

a)Muscle arms extend to nerves!

  1. Sensory structures
  2. Anterior

a)Amphids (chemosensory?)

Narrow canal leads to cell

  • Modified cilia: non-motile!
  • Non motile

b)Ocelli (some)

  1. Additional sensory structures on entire body

a)Cuticular bristles and papillae

  1. Caudal (on parasites)

a)Phasmids (chemosensory?)

  1. Movement
  2. Muscles
  3. Longitudinal muscles only

a)Several along body length

  1. No peristalsis!
  2. Must push against solid surface to move forward
  3. Elasticity of cuticle may aid in movement
  1. Note antagonistic muscle action
  2. Right contracted  left relaxed
  1. Reproduction
  2. Sexual reproduction
  3. Sexes separate
  4. Single pair of highly coiled gonads
  5. internal fertilization

a)Male has cuticular spicules

  1. sperm lack flagella (amoeboid)
  2. Oviparous or ovoviviparous
  3. High incidence of parthenogenesis

a)In some, mating occurs but sperm nucleus not used.

  1. Some hermaphrodites
  1. Parastic life cycles: next time!

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