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Nematodes. We’re Everywhere!. Objectives. Describe body form and support systems. Explain reproduction methods. Describe internal structures. Identify defense mechanisms. Differentiate between functional types. Body Form.

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We’re Everywhere!



  • Describe body form and support systems.

  • Explain reproduction methods.

  • Describe internal structures.

  • Identify defense mechanisms.

  • Differentiate between functional types.

Body form

Body Form

  • Nematodes, more commonly known as round-worms, have three basic body characteristics.

    • unsegmented: not divided into segments

    • bilaterally symmetric: body is identical on each side

    • triploblastic: consists of three primary germ layers the ectoderm, mesoderm and endoderm.

Support systems

Support Systems

  • They absorb oxygen through their skin in a process known as diffusion.

    • In diffusion, the oxygen passes over the germ layers from an area of high concentration to low.

  • Nematodes control movement through a hydrostatic skeletal system.

    • A fluid-filled cavity is surrounded by muscles. The fluid and surrounding muscles produce movement.

    • Nematodes are commonly called a “tube within a tube.”

  • Digestive system

    Digestive System

    • Roundworms are also characterized by a complete digestive system.

      • food processing occurs within the alimentary canal, running lengthwise through the body.

  • Their digestive system can be divided into three parts, the stomodeum, intestine, and proctodeum.

    • The stomodeum consists of the “mouth and lips”, buccal cavity, and the pharynx (esophagus).

    • The intestine functions by digesting, absorbing water and nutrients, and eliminating the residues of digestion.

    • The proctodeum serves as the anus and is where waste is excreted.

  • Nervous system

    Nervous System

    • The nematode nervous system consists of a set of neuronal processes that run lengthwise on the nematode body.

    • These processes consist of neurons that have a cell body also known as a neurocyte. A group of neurocytes is called a ganglion.

    • These ganglion connect to the nervering which surrounds the esophagus.

    Reproduction methods

    Reproduction Methods

    • Males are smaller than females and have a bent tail for holding the female for copulation.

    • During copulation, spicules are inserted into the genital pore of the female, enabling amoeboid sperm to crawl along the spicule.

    • Eggs may be embryonated or unembryonated, meaning that they may not yet be developed.

    Defense mechanisms

    Defense Mechanisms

    • The cuticle is the flexible outer covering which acts as an exoskeleton, allowing the nematode to maintain internal stability.

    • It is formed by secretion of the hypodermis.

      • The hypodermis is a thin cellular layer underlying the cuticle.

  • The cuticle functions as a barrier, a sensory array, and as a hydrostatic skeleton.

    • As a barrier it provides protection.

    • As a as sensory array it detects changes.

    • As a hydrostatic skeleton it acts as an antagonist to longitudinal muscles.

  • Free living species

    Free-Living Species

    • Free-living species have a wide range of food they consume, such as:

      • living tissues

      • small animals

      • dead organisms

      • fungi

      • algae

      • fecal matter

    Free living species1

    Free-Living Species

    • 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

    Parasitic Species

    • Parasitic nematodes can live off a wide variety of living organisms from plants to insects to humans.

    • They often lead very complicated lives in which they must transfer from different host species.

      • An appropriate example of this complicated lifestyle resides with the fig wasps along the Panama Canal.

      • Nematodes lay their eggs within the figs and hatch once the female fig wasps also emerge.

      • The nematodes penetrate the body cavity of the female wasp and slowly consume her from the inside once outside.

      • 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

    Fun Facts

    • Nematodes are the most abundant multicellular organism.

    • Some Nematodes can undergo cryptobiosis.

      • In cryptobiosis the nematodes alter their metabolism in response to a drastic environmental change (like freezing or extreme heat).

      • Essentially, the nematodes shut down their bodies and “wake up” when conditions are habitable again.

    • Would you like to take a guess at how large the biggest nematode ever recorded was?

    • Placentonema gigantissima, was a little over 27 feet long!

      • It was discovered inside the placenta of a sperm whale.

    • Nematodes can be as small as 0.01 inches.

    • They can be found in places like Antarctica and oceanic trenches.

    • One handful of soil contains thousands of roundworms

    Works cited

    Works Cited












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