Ch 11 Pseudocoelomates

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Ch 11 Pseudocoelomates soo-doe-see-low-mates
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Pseudocoelomates(Aschelminthes)

• 7 phyla
• Do not molt
• Rotifera
• Acanthocephala
• Molt
• Nematoda
• Nematomorpha
• Kinoryncha
• Loricifera
• Priapulida

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Phylogeny

• Two Hypothesis
• Phyla related based on anatomy, pseudocoelom,
  cuticle, muscular pharynx, and adhesive glands.
• Phyla not related, thus are polyphyletic absence
  in single unique feature ? independent evolution
  
• a. similarities result of convergent evolution
  in similar environments.

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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

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Pseudocoelomates

• Common characteristics
• First animal to posses a distinct body cavity,
  but they lack the peritoneal lining and membranes
  (mesenteries)
• Pseudocoelom- fluid filled, gelatinous substance,
  serves for circulation, aids in digestion, acts
  as hydroskeleton.

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• 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

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• Common characteristics
• Pseudocoelom
• Pseudocoelom is spacious, fluid-filled and
  Contains visceral organs
• No muscular tissue associated with gut tract
• No membranes suspend organs in body cavity

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• Common characteristics
• Eutely
• Eutely (thrift) a condition in which the number
  of cells is constant (i.e. C. elegans 959 adult)

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• Common characteristics
• complete digestive tract (mouth and anus)
• Found in most other higher animals

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Common characteristics

• Bilateral symmetry
• Unsegmented, tribploblastic, and cylindrical in
  cross section
• Protonephridia
• Some cephalization is evident (primitive brain,
  mouth, sense organs)
• Dioecious
• Complete digestive tract (mouth and anus)
• All have cuticle

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• 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

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Pseudocoelomates

• Organ systems present
• Digestive system
• Excretory system
• Nervous system
• Reproductive system
• Organ systems absent
• Circulatory system
• Respiratory system

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Phylum Rotifera
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Phylum Rotifera(non Molting)

• rota wheel (wave of beating cilia)
• fera bearer
• Freshwater, some marine
• B/w grains of sand
• Ciliated crown (corona)
• Food, locomotion
• (movie)

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Phylum Rotifera

• Mostly microscopic
• 1800 species
• Many resistant to desiccation
• dioecious

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Phylum Rotifera

• Brain
• Muscular pharynx- mastax
• Protonephridia with flame cells
• Pedal glands

Internal Anatomy of a Typical Rotifer
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Phylum Nematoda

• The roundworms

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Phylum Nematoda(Molt)

• 16,000 species
• 500,000 possible
• Cylindrical body (vermiform)
• Excretory system -renette
• Mostly dioecious
• Only longitudinal muscles
• Undulate/thrash around (dont crawl) movie

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Phylum Nematoda

• Noncellular cuticle with several layers
• Primary layers of cuticle- cortex, matrix layer
  and basal layer
• Maintains internal hydrostatic pressure
• Provides mechanical protection
• Resists digestion by host (in parasitic nematodes)

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Phylum Nematoda (contd)

• Found everywhere
• Oceans (free living and parasitic)
• Polar ice
• Hot springs
• Soil
• Some play an important role in nutrient recycling

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5 billion per acre
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Phylum Nematoda (contd)

• Eat just about every type of organic material
• Rotting substance
• Living tissue
• Parasites of nearly all plant and animal species!

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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?

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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

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Figure 11.10
Life cycle of Ascaris lumbicoides
Migrate to
Molt
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Pinworms

• Most common parasite in US
• 30 children 16 adults
• Large intestine
• Lay eggs (first-stage larva) in perianal area at
  night
• Itch and Spread
• Fecal oral route
• Larval molt four times in Small Intestines and
  migrate to large Intestines

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Figure 11.11
Pinworm life cycle
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Figure 11.13 (a)
Trinchinella spiralis the Porkworm
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Figure 11.13 (b)
Cyst Larvae in skeletal muscle
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Filarial Worms

• Elephantiatis
• 250 million people (tropics)
• Lives in lymphatic system
• Obstruct lymph to cause swelling

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Figure 11.15
Wuchereria spp. Filarial worms Causes
Elephantiasis
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Other parasitic nematodes

• Hookworms
• Dog heartworms
• Trichinella (causes trichinosis)

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• biomedical research
• C. elegans

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C. elegans

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

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• 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
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http//www.uoguelph.ca/gbarron/N-D20Fungi/n-dfun
gi.htm