Ch 11 Pseudocoelomates
“soo-doe-see-low-mates”
Acrobeles complexus
Pseudocoelomates
• 9 phyla:
– Rotifera- do not molt
(Lophotrochozoan)
– Acanthocephala
– Nematoda molt (Ecdysozoan)
–
–
–
–
–
Nematomorpha
Kinoryncha
Loricifera
Priapulida
Gastrotrichia
– Entoprocta
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
Pseudocoelomates
•
Common characteristics:
1. Pseudocoelom
2. Eutely
3. complete digestive tract (mouth and anus)
Acanthocephalans and nematomorphs do not
have a complete digestive tract
Common characteristics:
1) 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
Common characteristics:
1) Pseudocoelom
• No muscular tissue associated with gut
tract
•
No membranes suspend organs in body
cavity
• Pseudocoelom is spacious, fluid-filled
– Contains visceral organs
– Forms hydrostatic skeleton
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
Common characteristics:
2) Eutely
• Body composed of constant number of
somatic cells (or nuclei) in adults
Common characteristics:
3) complete digestive tract (mouth and anus)
• Most other higher animals
http://www.wormatlas.org/handbook/alimentary/alimentary2.htm
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?
Pseudocoelomates
• Organ systems present:
–
–
–
–
Digestive system
Excretory system
Nervous system
Reproductive system
• Organ systems absent:
– Circulatory system
– Respiratory system
Phylum Nematoda
The roundworms
Phylum Nematoda
• 12,000 species
– 500,000 possible
• Cylindrical body
• Mostly dioecious
• Only longitudinal muscles
– Undulate/thrash around
(don’t crawl) movie
Phylum Nematoda
• Noncellular cuticle with several layers
– Maintains internal hydrostatic pressure
– Provides mechanical protection
– Resists digestion by host (in parasitic nematodes)
Phylum Nematoda (cont’d)
• Found everywhere
– Oceans
– Polar ice
– Hot springs
– soil
5 billion per acre
Phylum Nematoda (cont’d)
• Eat just about
every type of
organic material
– Rotting substance
– Living tissue
• Parasites of
nearly all plant
and animal
species!
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
Pinworms
• Most common parasite in US
• 30% children; 16% adults
• Large intestine
• Lay eggs in anus at night
• Spread
– Fecal oral route
Filarial Worms
• “Elephantiatis”
• 250 million people (tropics)
• Lives in lymphatic system
• Obstruct lymph to cause
swelling
Microfilaria of Wuchereria bancrofti
Other parasitic nematodes
• Hookworms
• Dog heartworms
• Trichinella
(causes trichinosis)
• biomedical research
– C. elegans
C. elegans
• Free living nematode
• 959 cells
– Development of every
cell is known (movie)
• Genome sequenced
– NCBI
• C. elegans
• Nobel Prize (2002)
Brenner, Sulston and
Horvitz
– “Genetic regulation of organ
development and
programmed cell death”
Sydney Brenner
- C. elegans since 1963
http://www.nobel.se/medicine/laureates/2002/press.html
Phylum Rotifera
Phylum Rotifera
– rota= wheel
– fera= bearer
• Ciliated crown (corona)
– (movie)
http://www.microscopyu.com/galleries/dxm1200/images/collothecalarge.jpg
Phylum Rotifera
• Mostly microscopic
• 1800 species
• Many resistant to desiccation
• dioecious
http://micro.magnet.fsu.edu/primer/techniques/phasegallery/images/rotifer.jpg
Phylum Rotifera
• Aquatic (mostly freshwater)
– Protonephridia with flame cells
Internal Anatomy of a Typical Rotifer