Nematodes 2
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Transcript of Nematodes 2
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Nematodes
Were Everywhere!
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Objectives
o Describe body form and support systems.
o Explain reproduction methods.
o Describe internal structures.o Identify defense mechanisms.
o Differentiate between
functional types.
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Body Form
o Nematodes, more commonly known as round-
worms, have three basic body characteristics.o unsegmented: not divided into segments
o bilaterally symmetric: body is identical on each side
o triploblastic: consists of three primary germ layers
the ectoderm, mesoderm and endoderm.
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SupportSystems
o They absorb oxygen through their skin in aprocess known as diffusion.
o In diffusion, the oxygen passes over the germ layers
from an area of high concentration to low.o Nematodes control movement through a
hydrostatic skeletal system.
o A fluid-filled cavity is surrounded by muscles. Thefluid and surrounding muscles produce movement.
o Nematodes are commonly called a tube within atube.
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Digestive System
o Roundworms are also characterizedby a completedigestive system.
o food processing occurs within the alimentary canal,running lengthwise through the body.
o Their digestive system can be divided into threeparts, the stomodeum, intestine, and proctodeum.
o The stomodeum consists of the mouth and lips,buccal cavity, and the pharynx (esophagus).
o The intestine functions by digesting, absorbingwater and nutrients, and eliminating the residues ofdigestion.
o The proctodeum serves as the anus and is wherewaste is excreted.
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Nervous Systemo The nematode nervous
system consists of a set
of neuronal processes
that run lengthwise on
the nematode body.
o These processes consist
of neurons that have a
cell body also known as aneurocyte. A group of neurocytes is called a
ganglion.
o These ganglion connect to the nerve ring which
surrounds the esophagus.
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Reproduction Methods
o Males are smaller than females and have a bent
tail for holding the female for copulation.
o During copulation, spicules are inserted into the
genital pore of the female, enabling amoeboid
sperm to crawl along the spicule.
o Eggs may be embryonated
or unembryonated,meaning that they may
not yetbe developed.
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Defense Mechanismso The cuticle is the flexible outer covering which acts
as an exoskeleton, allowing the nematode to
maintain internal stability.
o It is formed by secretion of the hypodermis.o The hypodermis is a thin cellular layer underlying the
cuticle.
o The cuticle functions as a barrier, a sensory array,
and as a hydrostatic skeleton.o As a barrier it provides protection.
o As a as sensory array it detects changes.
o As a hydrostatic skeleton it acts as an antagonist to
longitudinal muscles.
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Free-Living Species
o Free-living species have a wide range of food they
consume, such as:
o living tissues
o small animals
o dead organisms
o fungi
o algae
o fecal matter
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Free-Living Species
o Marine nematodes have a large role in
decomposition and recycling. As a result of this
they tend to be extremely sensitive to pollution,
which drastically changes their environment.
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Parasitic Species
o Parasitic nematodes can live off a wide variety of living
organisms from plants to insects to humans.
o They often lead very complicated lives in which they
must transfer from different host species.o An appropriate example of this complicated lifestyle resides
with the fig wasps along the Panama Canal.
o Nematodes lay their eggs within the figs and hatch once the
female fig wasps also emerge.
o The nematodes penetrate the body cavity of the female wasp
and slowly consume her from the inside once outside.
o When the female fig wasp lands on a newly developing fig the
wasp dies and the life cycle for the nematode begins a new.
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Fun Facts
o Nematodes are the most abundant multicellular organism.
o Some Nematodes can undergo cryptobiosis.o In cryptobiosis the nematodes alter their metabolism in response to
a drastic environmental change (like freezing or extreme heat).
o Essentially, the nematodes shut down their bodies and wake upwhen conditions are habitable again.
o Would you like to take a guess at how large the biggestnematode ever recorded was?
o Placentonema gigantissima, was a little over 27 feet long!o It was discovered inside the placenta of a sperm whale.
o Nematodes can be as small as 0.01 inches.
o They can be found in places like Antarctica and oceanictrenches.
o One handful of soil contains thousands of roundworms
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Works Cited
o web.pml.ac.uk
o http://en.wikipedia.org/wiki/Roundworms
o www.eb.tuebingen.mpg.de
o www.emc.maricopa.edu
o www.dictionary.como www.oardc.ohio-state.edu
o ucdnema.ucdavis.edu/imagemap/nemmap/Ent156html/intro/nervous-system
o ucdnema.ucdavis.edu/imagemap/nemmap/ent156html/intro/cuticle
o www.biani.unige.cho http://books.google.com/books?id=JekumaoJYV8C&pg=RA1-
PA501&lpg=RA1-PA501&dq=nematode+dependent+wasps&source=web&ots=TskoskB10M&sig=3IsrzP67rCRu2QZFW7029MLogeg
o http://www.quizmoz.com/quizzes/Animal-Quizzes/n/Nematode-
Quiz.asp
