Transcript Platyhelminthes & Nematoda

The un-segmented worms
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GENERAL CHARACTERISTICS
18,500 species
Simplest animals with bilateral symmetry
Exhibit some cephalization
Three germ layers (i.e.:triploblastic)
Acoelomate: no mesodermal lined cavity
3 classes parasitic, 1 class free-living
Pharynx
(a) Digestive System
Excretory Canal
Gastrovascular Cavity
Excretory Pore
(b1) Excretory System
(b2) Nervous System
Nerve Cord
Chapter 22
Brain
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Because they are flat, flatworms have no
specialized circulation or respiration. They
simply use diffusion across body wall.
In addition to diffusion, flatworms use
protonephridia (simple kidney-like structure)
to osmoregulate (control water balance).
Within the protonephridia, there are beating
cilia which draws fluid through. Because this
looks like a flickering candle, these cells are
dubbed flame cells.
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Digestion: 1 way (like us!): Pharynx is on
underside of flatworm and sucks food into
the gastrovascular cavity.
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Intestine branches the length of the flatworm, so
digested food can be delivered to all body tissues
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Reproduction: Most flatworms are
simultaneous hermaphrodites. Each
individual can function as both male and
female. Although a single individual cannot
fertilize itself.
Movement: Secrete mucus and use cilia on
their epidermal cells to glide across bottom,
as well as muscle contractions which allows
them to twist and turn.
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Class Turbellaria-planarians, free-living, nonparasitic, live in moist environments
Class Trematoda-flukes, parasites that absorb
nutrients from the body of a host harming it,
may have more than 1 host
Class Cestoidea-tapeworms, parasitic, live
inside 1 or more hosts, contain flat segments
each with reproductive organs
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Class Turbellaria
16% of flatworms
 Most species are free living.
 Most live in marine environments
 Diet includes: bacteria, algae and invertebrates
 Considerable powers of regeneration in some
species
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Class Cestoda
Endoparasites: Internal parasites
 Celebrity cestoda: Tapeworm
 Hosts are primarily vertebrates.
 Extremely high specialization for parasitic lifestyle.
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 No ciliated epidermis.
 No mouth, instead has scolex studded with hooks and
suckers.
 Scolex attaches to the intestinal wall
 It is estimated that 135 million people are
infected with tapeworms.
 Symptoms include: Nausea, weakness, loss of
appetite, abdominal pain, diarrhea and weight
loss
 Most of the body is made up of repeating
reproductive segments called proglottids.
 A single proglottid may contain over 100,000
eggs!
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An intermediate host is required, such as a
cow, fish or pig.
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Class Trematoda
 Parasitic worms known as flukes.
 Some are ectoparasites parasites, living on
skin, mouth and gills of host.
 Celebrity Tremadode: Schistosoma, humans
are primary hosts.
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Schistosoma lay so many eggs in blood
vessels of the intestine that blood vessels
burst and eggs and blood are released into
intestine.
Nematoda
Rotifera
Nematoda
the pseudocoelomates
Platyhelminthes
Cnidaria
Porifera
unknown
common ancestor
Nemertea
Rotifera
• There are 9 different phyla that are classified as
pseudocoelomates.
•We are only covering 2 phyla:
Nematoda
Rotifera
Organ level of organization
Tissues are organized to for organs which are
used to accomplish physiological functions
Triploblastic
3 Germ Layers
3 Tissue Layers
endoderm
gastrodermis
mesoderm
mesoderm
ectoderm
epidermis
“false” body cavity
ectoderm
pseudocoelom
mesoderm
Gut
endoderm
the pseudocoelom is lined by mesoderm on ONE side only
the pseudocoelom
• is a closed, fluid filled cavity
• contains digestive, excretory, and reproductive
structures
• the fluid within acts as a circulatory system
• the fluid within acts as a hydrostatic skeleton against
which the muscles work
Bilateral Symmetry
• with anterior and posterior ends
Cephalization
• concentration of sensory organs in
the head of the animal
Digestive System
• complete (they have an anus!)
• some regional specialization
Circulation System
• no system (or organs)
• performed by the pseudocoelom fluid
Eutely
• each individual of a species has the same #
of cells
• growth occurs by cells getting bigger rather
than dividing
the roundworms
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Most abundant living animals include the
roundworms –closely related to insects than
others.
Cylindrical and bilateral body, a complete
gut and a false coelom filled by
reproductive organs. Have flexible cuticle –
undergo repetitive molting as it grows.
Free living sp that are decomposers and
agricultural pests.
Others are parasites to humans, dogs and
insects.
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Roundworms-small, cylindrical worms with pointed
heads and tapered tails
3 tissue layers
Complete digestive tract with mouth and anus
Digestion highly specialized
Free-living and non-parasitic roundworms are the
most abundant but parasitic types are hookworm,
pinworm, threadworm and trichinosis
Many are introduced through poorly cooked pork or
walk barefoot in infected areas
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Advanced gastrovascular cavity
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Tubular
Two openings
Advanced sensory "ganglionic brain"
Lack circulatory and respiratory systems
Depend on diffusion for gas exchange
Sexual reproduction
Most are harmless - Some parasitic
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Life Style
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Free-living
parasitic
Digestion
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complete system (have an anus)
some regional specialization (e.g. an
esophagus)
Skeletal system
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fluid in pseudocoelom acts as a hydrostatic
skeleton
Cuticle
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covers body (secreted by epidermis
&composed mostly of collagen)
functions as a primitive external skeleton
Movement
– longitudinal muscles ONLY
(results in “whiplike” motion)
– No external/internal cilia
 even sperm don’t have flagella
http://www.devgen.com/devpage/largeimage/wild.html
Nervous system
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cephalization, cerebral ganglia
dorsal and ventral nerve cords
Circulatory system
– No system (no organs)
– performed by fluid in pseudocoelom
Excretion
– Renette glands
Reproduction
Sexual
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usually dioecious
often the sexes are sexually dimorphic
(males and females look different)
Males often have a spicule
at the end of their tail used to insert their
sperm into the female
Reproduction
Sexual
 usually dioecious
 often the sexes are sexually dimorphic
 internal fertilization
 males have ameboid sperm
• There are >12,000 species that are found in almost
all habitats (marine, freshwater, underground, inside
plants and animals, etc…).
• They are also incredibly abundant. For example:
• a m² of soil may contain >4 million
nematodes
• a decomposing apple may contain >90,000
nematodes of a single species
• Many nematodes are important parasites of
both plants and animals.
parasite of
soybean plants
parasite of
tomato plants
Eye worm (Loa loa):
• transmitted by fly bites
• larvae go through bloodstream
• adults live in subcutaneous tissue
Intestinal roundworm (Ascaris):
• transmitted by contaminated food
• adults live in small intestine
• it’s estimated that 20% of world’s population is
infected (~1.3 billion people)
this intestine was completely blocked
Guinea worm (Dracunculus medinensis):
• transmitted by infected copepods in drinking water
• larvae move into the body cavity
• female adult migrates to the subcutaneous tissue, causes an
ulcer/blister, and releases eggs through hole when host comes in
contact with water
Guinea worm (Dracunculus
medinensis):
• traditionally removed by
winding the worm around a
matchstick over the course
of several days
• this may be the basis for
the Caduceus symbol used
in the medical field
Trichinella spiralis:
• causes Trichinosis
• transmitted by eating undercooked pork
• juveniles encyst within host muscle cells
juvenile
Host muscle
cell
Parasites
Heartworms (Dinofilaria immitis):
• The study of the model nematode C. elegans has resulted in
important discoveries in genetics and development.
the rotifers
The “wheel” animals
Feeding
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have a “crown” of cilia called a corona
the corona creates a
current to bring food into
the mouth
Feeding
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have a specialized feeding structure called
the:
mastax-trophi complex
modified jaws
within the mastax
a modified
muscular pharynx
Some of the trophi (jaws):
Life Style
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Free-living
Digestion
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complete system (have an anus)
some regional specialization (e.g.
mastax-trophi complex)
Skeletal system
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fluid in pseudocoelom acts as a
hydrostatic skeleton
Movement
– the corona
– pedal glands (produce adhesive), as
well as foot and toe (spurs) for
attachment to substrate
Nervous system
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cephalization, cerebral ganglia
dorsal and ventral nerve cords
Circulatory system
– no system (no organs)
– performed by fluid in pseudocoelom
Excretion
– protonephridia and flame cells
– cloacal bladder (collects wastes)
Sexual Reproduction
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complex life cycle with different types of eggs
usually dioecious but in some groups, males
are absent (parthenogenesis)
Parthenogenesis:
unisexual reproduction where females
produce offspring from unfertilized eggs
(virgin birth)
AMICTIC EGGS
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diploid
(mitotically
produced)
can’t be fertilized
develop into
diploid, amictic
females
MICTIC EGGS
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haploid (meiotically produced)
produced after some sort of
environmental stimulus (eg. high
density, change in temperature)
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if unfertilized, develop into
haploid males
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if fertilized, secrete a thick,
protective shell until the
environment is favorable
again, after which they
develop into diploid, amictic
females
• There are ~1500 species. Although they are found mainly in
freshwater habitats, there are a few marine rotifer species
and a couple of species are even found in mosses!
• Because of the reduced role of males in reproduction, most
males are incapable of feeding and do not even have a
digestive tract (they are just there for sperm delivery!).
• Males have never been recorded in Bdelloid rotifers. This
means they haven’t had sex in millions of years!
Loricifera
Nematomorpha
Kinorhyncha
Priapulida
Acanthocephala
Gastrotricha
Entoprocta
Rotifera
Nematoda
mastax-trophi
corona
no cilia
longitudinal muscles only
Platyhelminthes
Nemertea
Cnidaria
Porifera
complete digestive
system
organ level of organization
triploblastic
unknown
common ancestor