Nematodes

1. Nematodes We’re Everywhere!

2. Objectives • Describe body form and support systems. • Explain reproduction methods. • Describe internal structures. • Identify defense mechanisms. • Differentiate between functional types.

3. 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.

4. 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.”

5. 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.

6. 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.

7. 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.

8. 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.

9. 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

10. 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.

11. 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.

12. 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

13. Works Cited • 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/nervous-system • ucdnema.ucdavis.edu/imagemap/nemmap/ent156html/intro/cuticle • www.biani.unige.ch • http://books.google.com/books?id=JekumaoJYV8C&pg=RA1-PA501&lpg=RA1-PA501&dq=nematode+dependent+wasps&source=web&ots=TskoskB10M&sig=3IsrzP67rCRu2QZFW7029MLogeg • http://www.quizmoz.com/quizzes/Animal-Quizzes/n/Nematode-Quiz.asp