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

2. Architectural patterns of animals
Architectural patterns of animals. These basic body plans have been variously modivied during evolutoinary descent to fit aimals to a great variety of habitats. Ectoderm is shown in gray, mesoderm in red, and endoderm in yellow

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

5. 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
Plant ectoparasite
A. lumbricoides
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. 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: Organ systems absent:
Digestive system
Excretory system
Nervous system
Reproductive system
Organ systems absent:
Circulatory system
Respiratory system
All figures from

15. Phylum Nematoda
The roundworms

16. Phylum Nematoda 12,000 species Cylindrical body Mostly dioecious
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 1.2 billion people
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
Up to 1.2 cm

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

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

25. biomedical research
C. elegans

26. C. elegans Free living nematode 959 cells Genome sequenced
Development of every cell is known (movie)
Genome sequenced
NCBI
1090 generated. Exactly 131 programmed death

27. C. elegans Nobel Prize (2002) Brenner, Sulston and Horvitz
“Genetic regulation of organ development and programmed cell death”
Sydney Brenner
- C. elegans since 1963
Using the nematode C. elegans this year's Nobel Laureates have demonstrated how organ development and programmed cell death are genetically regulated. They have identified key genes regulating programmed cell death and demonstrated that corresponding genes exist also in higher animals, including man. The figure schematically illustrates the cell lineage (top left) and the programmed cell death (below) in C. elegans. The fertilized egg cell undergoes a series of cell divisions leading to cell differentiation and cell specialization, eventually producing the adult organism (top right). In C. elegans, all cell divisions and differentiations are invariant, i.e. identical from individual to individual, which made it possible to construct a cell lineage for all cell divisions. During development, 1090 cells are generated, but precisely 131 of these cells are eliminated by programmed cell death. This results in an adult nematode (the hermaphrodite), composed of 959 somatic cells.

28. Phylum Rotifera

29. Phylum Rotifera Ciliated crown (corona) rota= wheel fera= bearer
(movie)

30. 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

32. Nematode-destroying fungi