Transcript simple nervous

Phylum Platyhelminthes
Flatworms
Flatworms: The
Platyhelminthes
Acoelomates: no coelom
Bilateral symmetry
Cephalization: with simple nervous
system in the form of ganglia
knotted at head and extending the
body as a nerve cord.
Eye spots, ocelli, at anterior part of
the body called the head. Light
sensitive only.
Nerve knots on side of head in
planaria guide direction of
movement.
Pharynx , muscular tube, for all
processes in and out of the body.
Food in and waste out.
• Primitive kidneys called protonephridia,
end in flame cells.
• Flame cells remove excess water from the
body and excrete waste
• Use cilia on epidermis for moving across
surface. Muscle cells allow torsion
Reproduction
•Reproduce sexually
•Most are hermaphroditic
– Same individual has both male and female sex
organs
Worms line up side by side and exchange
packets of sperm. Self fertilize eggs.
Eggs laid in clusters and hatch in weeks.
Asexual by fission, individuals break apart and
make new worms.
• Three definite tissue layers:
–Epidermis
–Mesoderm
of muscles and
~
connective tissues
–Endoderm that forms gut
20,000 species in four classes
20,000 specied in four classes
Classes of Flatworms
• Turbellaria
– Free-living flatworms, mostly marine or fresh water
living.
• The flukes; have suckers to attach to host:
– Trematoda
• Parasitic
– Monogenea
• Parasitic
• Cestoda
– Tapeworms; intestinal parasites
Planaria
• Free living; a Turbellarian
• Carnivores, feed using their pharynx.
• No anus; undigested food/nutrients pass out of
pharynx.
• Flat body ensures excellent gas exchange
• Some metabolic waste excreted through
protonephridia that contain flame cells.
• Can learn; learning distributed throughout the
body because of knotted ganglia at anterior
portion of body.
Trematoda
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Parasitic flat worms
Infect internal organs of host
Some external parasites
Blood fluke Schistosoma is example
Reqires primary and secondary host
Common primary host is snail in rice
paddies. Humans eat snail by mistake and
get disease Shistosomiasis
A fluke
Complex structure
Large reproductive
Organs result in
Prolific production
of gametes
Sucker holds in place
Blood Fluke
The blood fluke
Very common and
serious human parasite
of tropical countries
Eggs passed in feces;
cycle through molluscan
intermediate
Cercariae from snail
burrow into skin of
humans in wet locations
Inset picture shows
adult male enfolding the
smaller female
Class Cestoda: The Tapeworms
• Flattened
• Intestinal parasites
• Have unique structure called scolex (see
Fig. 28-16) that holds onto inner lining with
many barbs.
• Segmented with many segments
– Each called proglottid
• Segmented with many segments
– Each called proglottid
• No mouth or digestive system
• Each proglottid absorbs nutrients across
body wall
• Life cycle of the beef tapeworm seen on
next slide
Beef Tape Worm
In muscle of cattle (1)
Encysted larvae (2)
Humans eat raw or incompletely
cooked meat (3)
Digestive juices dissolve cyst wall
Embryonic parasite develops
to maturity,reproduces sexually
and sheds proglottids filled
with zygotes (4)
Zygotes released in feces (5,6)
Zygotes ingested by cattle (1)
Kingdom Animalia
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Phylum: Platyhelminthes
Classes: Turbularia, Tremotoda, Cestoda
Phylum means flat
General description:
– Soft flattened body
– Tissues and internal organs/systems
– 3 germ layers, have mesoderm
– Bilateral symmetry
– Cephalization, head region with eye spots
•Examples:
•Turbularia: Planaria
•Tremotoda: blood fluke
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Schistosoma heptica
Cestoda: tapeworms
Movement: freely moving and parasitic
• Body Plan: Bilaterally symmetrical
• Triploblastic (endoderm, mesoderm,
ectoderm)
• Specialized cells:gastrovascular cavity
• Protonephridia, flame cells
• Eyespots in planaria
• Nutrition: carnivores and parasites
• Respiration: diffusion
• Circulation: none
• Excretion: flame cells
• Nervous system: ganglia in head region,
nerve net in body
–Light sensitive eye spots
–Reproduction: hermaphroditic, both sexes on
the same organism. Exchange sperm packets.