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Exploring Nematoda and Annelida: Fascinating Insights into Roundworms and Segmented Worms

Dive into the evolutionary relationships, body plans, feeding systems, and unique characteristics of Nematoda (roundworms) and Annelida (segmented worms) phyla. Discover the diverse classes within Annelida and various feeding strategies among different worm species. Unravel the mysteries of parasitic forms, reproduction, nervous systems, and locomotion mechanisms found in these intriguing invertebrates.

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Exploring Nematoda and Annelida: Fascinating Insights into Roundworms and Segmented Worms

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  1. Invertebrates 3 Nematoda and Annelida

  2. Phylum Nematoda:The roundworms

  3. Evolutionary relationships

  4. Nematode body cavity: pseudocoelom • Mesoderm on inside of body wall, but not surrounding gut

  5. Body plan • Feeding/digestive system • Nematodes suck! • Complete digestive system • Gas exchange • Body surface • Intestinal surface (minimal) • Body cavity (pseudocoelom) • No circulatory system • Excretory system/osmotic regulation • Exists, not well-understood • Locomotion: • Have only longitudinal muscles • Demo: The nematode swim!

  6. Body plan (cont.) • Nervous system • “Brain”: nerve ring • Four nerve cords (where?) • Ganglia along ventral cord • Unique connection of muscles and nerves • Sensory structures

  7. Reproduction, etc… • Reproduction • Sexes usually separate, but some hermaphrodites • Internal fertilization • Many parasitic forms • Trichina worms • Heartworms • River blindness • Elephantiasis • Also parasitic in plants

  8. Phylum Annelida:The segmented worms

  9. Evolutionary relationships

  10. Aceolomates, Pseudocoelomates and Coelomates

  11. Basic Annelida features • Have all features of protostomes (know!) • Have body segmentation (new feature) • Repetition of body parts • Similar structures found in each region • Some specialization of regions • Some continuous parts (digestive system)

  12. Annelid diversity Class Polychaeta Class Hirudinea Class Oligochaeta

  13. Digestive system Complete Specialized regions Circulation Closed system Multiple hearts Gas exchange Body surface Coelom Parapodia (Polychaetes) Excretory Metanephridia Body Plan (earthworm)

  14. Nervous system Brain (=cerebral ganglia) Ventral nerve cord (fused pair of cords) One ganglion per segment Movement Peristalsis Setae Body Plan (cont.)

  15. Feeding in different classes • Class Oligochaeta: Earthworms • Earth suckers (create vacuum by expanding muscular pharnyx) • Why important in ecosystem? • Class Polychaeta: Marine segmented worms • Many are tentacle feeders • Many other feeding modes • Class Hirudinea: Leeches • Food suckers (create vacuum by expanding pharynx, digestive tract) • How do blood sucking leeches feed?. • What three substances do blood sucking leeches secrete to aid in the process? • NOTE: Not all leeches are blood suckers!

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