Transcript Ch 15 Pseudocoelomate Animals

Ch 11 Pseudocoelomates
“soo-doe-see-low-mates”
Acrobeles complexus
Pseudocoelomates
(Aschelminthes)
• 7 phyla:
Do not molt
– Rotifera
– Acanthocephala
Molt
– Nematoda
– Nematomorpha
– Kinoryncha
– Loricifera
– Priapulida
Phylogeny
Two Hypothesis
1. Phyla related based on anatomy,
pseudocoelom, cuticle, muscular pharynx,
and adhesive glands.
2. Phyla not related, thus are polyphyletic
absence in single unique feature 
independent evolution
a. similarities result of convergent evolution in
similar environments.
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
Pseudocoelomates
•
Common characteristics:
1. First animal to posses a distinct body cavity,
but they lack the peritoneal lining and
membranes (mesenteries)
2. Pseudocoelom- fluid filled, gelatinous
substance, serves for circulation, aids in
digestion, acts as hydroskeleton.
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
• Pseudocoelom is spacious, fluid-filled and
Contains visceral organs
•
•
No muscular tissue associated with gut
tract
No membranes suspend organs in body
cavity
Common characteristics:
2) Eutely
• Eutely (thrift) a condition in which the
number of cells is constant (i.e. C. elegans
= 959 adult)
Common characteristics:
3) complete digestive tract (mouth and anus)
• Found in most other higher animals
http://www.wormatlas.org/handbook/alimentary/alimentary2.htm
Common characteristics:
1. Bilateral symmetry
2. Unsegmented, tribploblastic, and cylindrical in
cross section
3. Protonephridia
4. Some cephalization is evident (primitive brain,
mouth, sense organs)
5. Dioecious
6. Complete digestive tract (mouth and anus)
7. All have cuticle
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
Pseudocoelomates
• Organ systems present:
–
–
–
–
Digestive system
Excretory system
Nervous system
Reproductive system
• Organ systems absent:
– Circulatory system
– Respiratory system
Phylum Rotifera
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)
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
• Brain
• Muscular pharynx- mastax
• Protonephridia with flame
cells
• Pedal glands
Internal Anatomy of a Typical Rotifer
Phylum Nematoda
The roundworms
Phylum Nematoda
(Molt)
• 16,000 species
– 500,000 possible
• Cylindrical body
(vermiform)
• Excretory system -renette
• Mostly dioecious
• Only longitudinal muscles
– Undulate/thrash around
(don’t crawl) movie
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)
Phylum Nematoda (cont’d)
• Found everywhere
– Oceans (free
living and
parasitic)
– Polar ice
– Hot springs
– Soil
Some play an
important role in
nutrient recycling
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!
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?
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
Life cycle of Ascaris lumbicoides
Figure 11.10
Migrate to
Molt
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
Pinworm life cycle
Figure 11.11
Trinchinella spiralis: the Porkworm
Figure 11.13 (a)
Figure 11.13 (b)
Cyst Larvae in skeletal muscle
Filarial Worms
• “Elephantiatis”
• 250 million people (tropics)
• Lives in lymphatic system
• Obstruct lymph to cause
swelling
Microfilaria of Wuchereria bancrofti
Figure 11.15
Wuchereria spp. : Filarial worms
Causes Elephantiasis
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