1. Lecture 12: Phylum Nematoda (Nemata) The Nematodes
Invertebrate Zoology
Lecture 12: Phylum Nematoda (Nemata)
The Nematodes

2. Lecture outline Phylum Nematoda (Nemata) Diversity Phylogeny (briefly)
Bauplan Basics
Feeding
Circulation/Gas Exchange
Osmoregulation/Excretion
Nervous System
Movement
Reproduction

3. Diversity More individual nematodes than members of any other phyla?
Free-living forms found in nearly every environment
Free-living marine & freshwater
Between grains of beach sand
Key soil dwellers (nutrient processing)
Polar ice fields
Key plant & animal parasites

4. Phylogeny: Hypothesis 1 Based on body plan & development

5. Nematoda cross-section: Note muscles, pseudocoelom & cuticle

6. Detour: Other Blastocoelomates
Rotifera, Gastrotricha, Kinorhyncha, Nematomorpha, Priapula

7. Phylogeny: Hypothesis 2 Based on molecular data, cuticle features

8. Bauplan basics Protostome features include No spiral cleavage
Triploblastic (distinct mesoderm  muscles)
Bilateral symmetry & cephalization
Cell fate is determinate
No spiral cleavage
Cleavage pattern unique to Nematoda
Blastocoel forms blastocoelom (=pseudocoelom)
Feature shared by several phyla

9. Bauplan basics Cuticle In common with Arthropod cuticle:
Contains chitin
Secreted by epidermis
Several layers
Molts with growth
Ecdysone is key hormone
Fibers form flexible coil  elastic qualities for movement
Varies in appearance

10. Feeding/Digestion Simple mouth, or with stylet, teeth, jaws, etc…
Muscular pharynx lined with cuticle
Use of suction
Digestive system usually simple, not highly branched
Intestinal microvilli increase surface area
Some with bacterial symbionts & reduced digestive system

11. Feeding/Digestion

12. Gas exchange Body surface Pseudocoelomic (=blastocoelomic) cavity
Exchange between pseudocoelomic (=blastocoelomic) fluid and organs
No circulatory system

13. Osmoregulation/excretion
System of lateral cords connected to a large cell ("renette")
Associated with digestive system
Not well-studied
Empties via excretory pore
Excretion also via the digestive system

14. Nervous system Organization Nerve ring
Plus associated ganglia
Sensory nerve input (from head)
Four major nerve cords: 1 dorsal, 1 ventral, 2 lateral
Ventral cord may be fused & with ganglia (as in Annelida and Arthropoda)
Connection of longitudinal muscles is unique
Muscle arms extend to nerves!

15. Nervous system

16. Muscle arms attach to dorsal and ventral nerve cords

17. Sensory structures Anterior
Amphids (chemosensory?)
Narrow canal leads to cell
Modified cilia: non-motile!
Non motile
Ocelli (some)
Additional sensory structures on entire body
Cuticular bristles and papillae
Caudal (on parasites)
Phasmids (chemosensory?)

18. Movement Muscles Longitudinal muscles only No peristalsis!
Several along body length
No peristalsis!
Must push against solid surface to move forward
Elasticity of cuticle may aid in movement

19. Movement Note antagonistic muscle action
Right contracted  left relaxed

20. Reproduction Sexual reproduction Sexes separate
Single pair of highly coiled gonads
internal fertilization
Male has cuticular spicules
sperm lack flagella (amoeboid)
Oviparous or ovoviviparous
High incidence of parthenogenesis
In some, mating occurs but sperm nucleus not used.
Some hermaphrodites

22. Parasitic life cycles
Next time!