live in temperate regions in many parts of the world (Nicholas 1975).
are terrestrial organisms. They live primarily in soil (Lee & Atkinson 1977). The soil must have a constant level of moisture, so that the worm can move in the film of water and draw water from the soil. The soil must also have a moderate oxygen content. Worms may not be able to penetrate soils with high clay content. For ideal movement, the worm should be about three times as long as the diameter of the soil particles ( Nicholas 1975). Worms are also found in or on rotting vegetation above ground (Edgley 1999).
have elongated cylindrical bodies, tapered at both ends, with smooth skin, no segmentation, and no appendages. Adults grow to approximately 1mm in length. Exactly 959 cells compose , and their bodies are transparent; therefore, individual cells are easily observed with a microscope (Edgley 1999).
have two naturally occurring sexes, a male and a self-fertilizing hermaphrodite; females do not naturally occur. The majority of individuals are hermaphrodites; males usually comprise no more than 0.20% of the natural population. The number of males can be increased, however, by raising the temperature at the onset of sexual maturity (Nicholas 1975). Hermaphrodites are protandrous; the individuals produce sperm first and then produce eggs (Blaxter 1999). Most commonly, worms will simply fertilize their own eggs (Bird 1991). However, the males that do exist copulate with hermaphrodites, thus mixing up the gene pool in the population (Nicholas 1975). Eggs are laid within two to three hours of fertilization and hatch approximately twelve hours later. The worms develop into adults in four larval stages; this generally takes about three days when the temperature ranges from 20 to 25 degrees Celsius (Blaxter 1999). Temperature plays a major role in the development of . The worms' average lifespan is two to three weeks (Edgley 1999).
Images of http://www.mcb.arizona.edu/Wardlab/gallery.html (Muhlrad 1998)and sperm:
- Average lifespan
- 0.16 years
- Average lifespan
possess a simple brain and a nervous system (Malakhov 1994). They have relatively simple behavior; however, they are capable of rudimentary learning (Edgley 1999). The worms have basic tactile senses that allow them to determine their surroundings (Lee & Atkinson 1977). Most often use chemosensation and a strong sense of olfaction to gain information from their environment; the worms are very receptive to chemical signals that guide them to food, help them avoid toxins, find mates, and avoid predators (Troemel 1999). There is no need for a strong visual sense due to the dark environment in which they live; however, there is some evidence that the worms do respond minimally to light (Lee & Atkinson 1977). The worms are free-living and move throughout their environment; they live as individuals.
are bacteriovorous; they feed on various types of bacteria that live in soil and on rotting vegetation. They feed by ingesting bacteria in suspension or on detritus (Nicholas 1975).
Economic Importance for Humans: Positive
are used often in scientific research; they are considered a model organism and are easy to study due to their transparency. They are bred for use as laboratory specimens.
Economic Importance for Humans: Negative
This species has no known negative impact on humans.
are not endangered or threatened; they are found in large numbers in nature.
are often called or simply 'the worm' because they are a model species. are the first multicellular organisms to have their complete genome sequenced; their genome consists of six chromosomes (Blaxter 1999). The genes of the worm are studied to determine how the complex processes of embryogenesis, development, disease, and aging occur. This research is leading to a better understanding of the specific roles of genes in other organisms, including humans (Edgley 1999). For example, scientists are investigating the role that different genes play in the aging process of with the hope that much of what they learn will lead to a better understanding of the complex process of aging in humans. Scientists are also experimenting with various ways to slow or reverse the aging process; techniques developed could then be tested in humans (Blaxter 1999).
Image of http://www.soton.ac.uk/~djab/ce.htm (Avery 2000):
Meghan Oswald (author), University of Michigan-Ann Arbor, Phil Myers (editor), Museum of Zoology, University of Michigan-Ann Arbor.
Avery, L. 2000. "Caenorhabditis elegans" (On-line). Accessed March 22, 2000 at http://www.soton.ac.uk/~djab/ce.htm.
Bird, A., J. Bird. 1991. The Structure of Nematodes, Second Edition. New York: Academic Press, Inc..
Blaxter, M. 1999. "The Genetics of Caenorhabditis elegans" (On-line). Accessed March 22, 2000 at http://www.ed.ac.uk/~mbx/C_elegans/Ce_intro.html.
Edgley, M. 1999. "Introduction to Caenorhabditis elegans" (On-line). Accessed March 22, 2000 at http://www.biotech.missouri.edu/Dauer-World/Wormintro.html.
Lee, D., H. Atkinson. 1977. Physiology of Nematodes, Second Edition. New York: Columbia University Press.
Malakhov, V. 1994. Nematodes: Structure, Development, Classification, and Phylogeny. Washington: Smithsonian Institution Press.
Muhlrad, P. 1998. "Worm Sperm" (On-line). Accessed March 22, 2000 at http://www.mcb.arizona.edu/Wardlab/gallery.html.
Nicholas, W. 1975. The biology of free-living nematodes. Oxford, England: Clarendon Press.
Troemel, E. 1999. Chemosensory signaling in C. elegans. BioEssays, 21: 1011-1020.
Wood, W. 1988. The Nematode Caenorhabditis elegans. New York: Cold Spring Harbor Laboratory Press.