Ch 11 Pseudocoelomates “soo-doe-see-low-mates”

1. Acrobeles complexus Ch 11 Pseudocoelomates “soo-doe-see-low-mates”

4. Pseudocoelomates • 9 phyla: • Rotifera- do not molt (Lophotrochozoan) • Acanthocephala • Nematoda molt (Ecdysozoan) • Nematomorpha • Kinoryncha • Loricifera • Priapulida • Gastrotrichia • Entoprocta

5. Plant ectoparasite A. lumbricoides Pseudocoelomates • A heterogeneous group: • Size: microscopic  several meters • some are exclusively marine; some (e.g., nematodes) live in a variety of habitats, esp. soil); and some are exclusively parasitic pinworms

6. Pseudocoelomates • Common characteristics: • Pseudocoelom • Eutely • complete digestive tract (mouth and anus) Acanthocephalans and nematomorphs do not have a complete digestive tract

7. Common characteristics: • Pseudocoelom • body cavity (pseudocoelom/ pseudocoel) • a space b/w gut and mesodermal components of body wall • Body cavity is not lined with a mesodermal sheet • Does not cover inner surface of body wall

8. Common characteristics: • Pseudocoelom • No muscular tissue associated with gut tract • No membranes suspend organs in body cavity

9. Pseudocoelom is spacious, fluid-filled • Contains visceral organs • Forms hydrostatic skeleton

10. Evolutionary advantages of pseudocoel: • Greater freedom of movement • Space for development and differentiation of organ systems (ie. digestive, excretory) • differentiation: process by which cells become different, specialized • Simple means of circulation/distribution of materials throughout body • Storage place for waste products to be discharged to outside • Hydrostatic skeleton • Fluid enclosed by muscular wall  support

11. Common characteristics: • Eutely • Body composed of constant number of somatic cells (or nuclei) in adults

12. http://www.wormatlas.org/handbook/alimentary/alimentary2.htm Common characteristics: • complete digestive tract (mouth and anus) • Most other higher animals

13. Do these questions now… • What type of germ layer lines the pseudocoelom in nematode embryos? • What organ systems are present/absent in pseudocoelomates • What are the advantages of having a pseudocoelom vs. no coelom?

14. Pseudocoelomates • Organ systems present: • Digestive system • Excretory system • Nervous system • Reproductive system • Organ systems absent: • Circulatory system • Respiratory system

15. Phylum Nematoda The roundworms

16. Phylum Nematoda • 12,000 species • 500,000 possible • Cylindrical body • Mostly dioecious • Only longitudinal muscles • Undulate/thrash around (don’t crawl) movie

17. Phylum Nematoda • Noncellular cuticle with several layers • Maintains internal hydrostatic pressure • Provides mechanical protection • Resists digestion by host (in parasitic nematodes)

18. Phylum Nematoda (cont’d) • Found everywhere • Oceans • Polar ice • Hot springs • soil

19. 5 billion per acre

20. Phylum Nematoda (cont’d) • Eat just about every type of organic material • Rotting substance • Living tissue • Parasites of nearly all plant and animal species!

21. Ascaris lumbricoides • Human parasite • Up to 30cm long • 1.2 billion people • Many in southeast US • Females lay 200,000 eggs a day • Unsanitary habits contaminate ground • Ingest eggs • Hatch  bury into veins  lungs  pharynx • Swallowed  intestine

22. Pinworms • Most common parasite in US • 30% children; 16% adults • Large intestine • Lay eggs in anus at night • Spread • Fecal oral route

23. Microfilaria of Wuchereria bancrofti Filarial Worms • “Elephantiatis” • 250 million people (tropics) • Lives in lymphatic system • Obstruct lymph to cause swelling

24. Other parasitic nematodes • Hookworms • Dog heartworms • Trichinella (causes trichinosis)

25. biomedical research • C. elegans

26. C. elegans • Free living nematode • 959 cells • Development of every cell is known (movie) • Genome sequenced • NCBI

27. Sydney Brenner • - C. elegans since 1963 • C. elegans • Nobel Prize (2002)Brenner, Sulston and Horvitz • “Genetic regulation of organ development and programmed cell death” http://www.nobel.se/medicine/laureates/2002/press.html

28. Phylum Rotifera

29. http://www.microscopyu.com/galleries/dxm1200/images/collothecalarge.jpghttp://www.microscopyu.com/galleries/dxm1200/images/collothecalarge.jpg Phylum Rotifera • rota= wheel • fera= bearer • Ciliated crown (corona) • (movie)

30. http://micro.magnet.fsu.edu/primer/techniques/phasegallery/images/rotifer.jpghttp://micro.magnet.fsu.edu/primer/techniques/phasegallery/images/rotifer.jpg Phylum Rotifera • Mostly microscopic • 1800 species • Many resistant to desiccation • dioecious

31. Phylum Rotifera • Aquatic (mostly freshwater) • Protonephridia with flame cells Internal Anatomy of a Typical Rotifer