Nematodes
We’re Everywhere!
Objectives
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Describe body form and support systems.
Explain reproduction methods.
Describe internal structures.
Identify defense mechanisms.
Differentiate between
functional types.
Body Form
o Nematodes, more commonly known as roundworms, 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.
Support Systems
o They absorb oxygen through their skin in a
process 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. The
fluid and surrounding muscles produce movement.
o Nematodes are commonly called a “tube within a
tube.”
Digestive System
o Roundworms are also characterized by a complete
digestive system.
o food processing occurs within the alimentary canal,
running lengthwise through the body.
o Their digestive system can be divided into three
parts, 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, absorbing water
and nutrients, and eliminating the residues of
digestion.
o The proctodeum serves as the anus and is where
waste is excreted.
Nervous System
o 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 a
neurocyte. A group of neurocytes is called a
ganglion.
o These ganglion connect to the nerve ring which
surrounds the esophagus.
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 yet be developed.
Defense Mechanisms
o 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.
Free-Living Species
o Free-living species have a wide range of food they
consume, such as:
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living tissues
small animals
dead organisms
fungi
algae
fecal matter
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.
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 anew.
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 up”
when conditions are habitable again.
o Would you like to take a guess at how large the biggest
nematode 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 oceanic
trenches.
o One handful of soil contains thousands of roundworms
Works Cited
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web.pml.ac.uk
http://en.wikipedia.org/wiki/Roundworms
www.eb.tuebingen.mpg.de
www.emc.maricopa.edu
www.dictionary.com
www.oardc.ohio-state.edu
ucdnema.ucdavis.edu/imagemap/nemmap/Ent156html/intro/ner
vous-system
ucdnema.ucdavis.edu/imagemap/nemmap/ent156html/intro/cuti
cle
www.biani.unige.ch
http://books.google.com/books?id=JekumaoJYV8C&pg=RA1PA501&lpg=RA1PA501&dq=nematode+dependent+wasps&source=web&ots=Tskos
kB10M&sig=3IsrzP67rCRu2QZFW7029MLogeg
http://www.quizmoz.com/quizzes/Animal-Quizzes/n/NematodeQuiz.asp