Nematodes

We’re Everywhere!

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.

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 sideo 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 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 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 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.

Free-Living Species

o Free-living species have a wide range of food they consume, such as:o living tissues o small animalso dead organismso fungio algaeo 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 Factso 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 Citedo web.pml.ac.uko http://en.wikipedia.org/wiki/Roundwormso www.eb.tuebingen.mpg.deo www.emc.maricopa.eduo www.dictionary.como www.oardc.ohio-state.eduo ucdnema.ucdavis.edu/imagemap/nemmap/Ent156html/intro/ner

vous-systemo 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