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Mapping body plan characters
on the tree
Animal diversity 2 - Animals
without a coelom
Key concepts
• Simple animals may be
evolutionarily successful, have
diverse life styles and behavior!
• Basic biology of
Porifera/ Cnidaria/
Platyhelminthes/ Nematoda
PROTOSTOMES
NEMATODA
PLA
TYH
RIF
INT
HE
ERA
ELM
PO
S
RY
RIA MET
IDAL SYM
CN
DIA
RA
DA
PO
RO A
TH
D
AR NELI
CA
AN L L U S
MO MOUTH AND ANUS
DEUTEROSTOMES
M
ER
OD
A
HIN
EC RDAT
O
CH
AT
A
TRUE COELOM
MOUTH AND ANUS
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BILATERAL SYMMETRY
TISSUES
EXTRACELLULAR DIGESTION
PROTISTA MULTICELLULARITY
Today: phyla without a true coelom
Diversity of Sponges
A. Body plan cells in
extracellular
matrix, tube
structure
with flow of
water
bringing
food to cells
PROTOSTOMES
NEMATODA
PLA
TYH
INT
HE
ERA
ELM
RIF
S
RY
RIA MET
IDA YM
CN DIAL S
RA
PO
DA
PO
RO A
TH
D
AR NELI
CA
AN L L U S
MO MOUTH AND ANUS
DEUTEROSTOMES
MA
ER
OD
HIN ATA
C
E
D
OR
CH
TA
TRUE COELOM
MOUTH AND ANUS
BILATERAL SYMMETRY
TISSUES
EXTRACELLULAR DIGESTION
PROTISTA MULTICELLULARITY
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B. Feeding
If choanocytes specialized for
feeding, how are other cell types
nourished?
via another cell type
- amoeboid cells
that move
throughout the
sponge, collecting
and further
digesting material
from choanocytes,
then passing it on
to other cells...
2
Diversity of Sponges
C. Reproduction
Asexual - branches may ‘pinch’ off and
regenerate
Sexual - most are hermaphrodites
Hermaphrodite - single individual produces
both male and female gametes
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Diversity of Sponges
Sperm are produced
from modified
choanocytes, released
into the environment
Choanocytes of other
sponges ‘capture
sperm’ in intracellular
capsules, then
transform into
migrating amoeboid
cells, carry sperm to an
egg!
Diversity of Sponges
The zygote (fertilized
egg) gives
rise to swimming
larva with choanocytes on
outside for
movement
A ‘smoking sponge’
releasing sperm
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Diversity of Sponges
Diversity of Cnidaria
C. Reproduction
Larva eventually settles, gives rise to
mature sponge
Two basic body forms
The polyp and the medusa - a
sedentary and mobile form
Polyp
Medusa
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Many cnidarians have both forms in their
life cycle, in others, one form
predominates
Which form predominates in jellyfish? In
sea anenomes? In coral?
Polyp
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Diversity of Cnidaria
Feeding
Adaptations for feeding and defense
- nematocysts - organelles that
function like miniature harpoons
Medusa
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Nematocysts
Trigger senses ‘foreign’ chemical profile
‘Harpoon’ released - can pierce a crab shell
Releases toxin - some species
have toxins fatal to humans
a
b
Diversity of Cnidaria
‘harpoon’
trigger
What do cnidarians use their
nematocysts for?
Capturing prey
Defense against predators
Defending territories (video
segment)
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Corals in particular…
Corals - polyp-form cnidarians, live in
large colonies, and secrete calcium
carbonate
When old polyps die, new ones build on
top
Diversity of Cnidaria:Corals in
particular…
Corals - polyp-form cnidarians, live in large
colonies, and secrete calcium carbonate
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Corals in particular
Diversity of Cnidaria
Where are the autotrophs in the coral reef
community? Corals live in shallow, clear,
nutrient-poor water...
Corals get much of their energy from
photosynthesizing plant-like protists “zooxanthellae” that live within their
cells
A coral reef is millions of coral
skeletons with living ones on the
periphery
Coral polyps
with
zooxanthellae
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Corals in particular
Diversity of Cnidaria
Environmental threats
to the coral zooxanthelle
interaction
Ocean pollution - light
can’t penetrate
cloudy waters
“Coral bleaching-”
corals lose their
zooxanthellae - a
recent serious
problem
Zooxanthellae are dinoflagellates that have
developed a mutualism with corals
Mutualism; interaction between species in
which both partners benefit
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Coral bleaching: The “adaptive
bleaching hypothesis”
Coral bleaching: What causes it?
Various factors, pollution, UV
irradiation, and most importantly,
heat
Because of global warming, some
predictions that coral reef
communities may be extinct within
50 years
But there’s some
hope the corals
are ahead of us in
solving this problem
Bleaching can be adaptive if
corals give up
zooxanthellae adapted to
old environment and pick
up new ones, with for
example, increased heat
tolerance
Some evidence for this but
still controversial
And it’s a high risk strategy corals have a limited
amount of time to reaquire
zooxanthellae before
they’re dead
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Dead coral being
colonized by algae
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Flatworms (Platyhelminthes) and
Roundworms (Nematoda)
Diversity of Cnidaria
Reproduction
Asexual reproduction - budding off
from polyps
Sexual reproduction - fertilized eggs
give rise to mobile, planktonic
forms
Plankton - small ocean organisms
that drift with water movement
PROTOSTOMES
NEMATODA
PLA
TYH
RIF
INT
HE
ERA
ELM
PO
S
RY
RIA MET
IDAL SYM
CN
DIA
RA
DA
PO
RO A
TH
D
AR NELI
CA
AN L L U S
MO MOUTH AND ANUS
DEUTEROSTOMES
MA
ER
OD
HIN ATA
C
E
D
OR
CH
TA
TRUE COELOM
MOUTH AND ANUS
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BILATERAL SYMMETRY
TISSUES
EXTRACELLULAR DIGESTION
PROTISTA MULTICELLULARITY
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Platyhelminthes
Platyhelminthes
Body plan
Feeding
Some free-living, many parasites
i. Some of the parasites with complex life
cycles: several different forms and more
than one host
No body cavity
In most mouth but no anus
Lack circulatory, respiratory
system, absorb O2 through
body wall
Movement?
slowly, through muscle
contraction
and/or beat cilia in slime trail!
Human liver fluke
must pass
through two other
hosts to complete
life cycle
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The platyhelminth parasite
Schistosoma
Platyhelminthes
Example of a human platyhelminthes
parasite: Schistosoma
Humans (where parasite reproduces)
the
definitive host
1) Parasite
Snails the intermediate host eggs shed
1) Parasite
eggs shed
in human
waste,
gets into
water
4) Burrow
into human
skin, infect
organs,
reproduce
in human
waste,
gets into
water
2) Eggs hatch, infect snails
3) Snails shed
swimming stage
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4) Burrow
into human
skin, infect
organs,
reproduce
The platyhelminth parasite,
Schistosoma
- causes schistosomiasis
- found throughout tropical Asia, subSaharan Africa, mid-East and Latin
America
- 200 million people infected, chronic
infection damages the liver, intestines,
lungs, 20 million develop ‘severe
consequences’
- What changes could help reduce
disease transmission?
2) Eggs hatch, infect snails
3) Snails shed
swimming stage
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Platyhelminthes
Body plan
Feeding
Reproduction
- some asexual - e.g. can cut
Planaria in two
- sexual, most hermaphrodites two hermaphrodites lie next to each other,
each donates sperm to the other’s egg sac
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Nematoda - roundworms
Nematoda - roundworms
Body plan
- very simple - “a tube within a tube”
Body plan
Have a pseudocoelom for body
cavity
Mesoderm lines
the body wall but
doesn’t surround
the gut
Have a one-way digestive system: a
mouth and an anus
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Nematoda - roundworms
Nematoda - roundworms
20K species, range in length
from 0.3 mm to 8 m (in whale
placenta *)
Feeding
Many free living decomposers
and
parasites of almost everything plants and animals
* What was it doing there?
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On cooking pork...
Nematoda - roundworms
Trichinella, a roundworm parasite of
mammals, including rodents, pigs and
humans
Pigs get infected from eating uncooked
meat scraps or from rodent
contamination, humans from eating
undercooked pork
Feeding
Many free living decomposers
and
parasites of everything - plants
and animals
Example - Trichinella
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On cooking pork...
On cooking pork...
Trichinosis not very common any more
In 1940, 16% of US human population
infected
In 1970, 4%
In 1991-1996, average of 38 cases per year
Why the improvement?
No raw meat fed to hogs, rodent control,
stringent inspections, and freezing and
thorough cooking of pork more common
Still a concern with wild game, esp. bear
meat
•Trichinella worms lay eggs in intestine,
young larvae travel through arteries and
encyst in muscles - can live for years
• Short-term symptoms - abominal pain,
vomiting, fatigue and fever
• Then, headaches, fever, aching joints
and muscles
• Later most symptoms subside - chronic
infection
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What about Wilbur?
Nematoda - roundworms
When parasites are our allies
- the use of insect-parasitic
nematodes for control of pests
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Nematodes that cause river
blindness, elephantiasis in humans
also have mutualist bacteria
Nematoda - roundworms
Nematode parasites sometimes have
mutualistic bacterial associates
Insect-parasitic nematodes release
bacteria in the host, the bacteria kill
the host
Some of these
bacteria are
luminescent!
Just recently led to new therapies
with antibiotics
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Nematoda - roundworms
Nematoda - roundworms
Reproduction
Sexual - some species have
both sexes, some are
hermaphrodites
Reproduction
The record for reproductive output?
Ascaris the parasitic roundworm,
produces 100,000 - 200,000 eggs
per day!
Assuming population isn’t growing,
what does this say about mortality
of immature stages?
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