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?Earthworms
Lumbricus terrestris, the Common European Earthworm
Lumbricus terrestris, the Common European Earthworm
Scientific classification
Kingdom: Animalia
Phylum: Annelida
Class: Clitellata
Subclass: Oligochaeta
Order: Haplotaxida
Suborder: Lumbricina
Families

  Acanthodrilidae
  Ailoscolecidae
  Alluroididae
  Almidae
  Criodrilidae
  Eudrilidae
  Exxidae
  Glossoscolecidae
  Lumbricidae
  Lutodrilidae
  Megascolecidae
  Microchaetidae
  Ocnerodrilidae
  Octochaetidae
  Sparganophilidae

Earthworm is the common name for the largest members of the Oligochaeta (which is either a class or subclass depending on the author) in the phylum Annelida. In classical systems they were placed in the order Opisthopora, on the basis of the male pores opening to the outside of the body posterior to the female pores, even though the male segments are anterior to the female. Cladistic studies have supported placing them instead in the suborder Lumbricina of the order Haplotaxida. Folk names for earthworm include "dew-worm", "rainworm", "night crawler" and "angleworm".

Earthworms are also called megadriles (or big worms), as opposed to the microdriles, which include the families Tubificidae, Lumbriculidae, and Enchytraeidae, among others. The megadriles are characterized by having a multilayered clitellum (which is much more obvious than the single-layered one of the microdriles), a vascular system with true capillaries, and male pores behind the female pores.

OverviewEdit

There are over 5,500 named species known worldwide, everywhere but polar and arid climates. They range in size from two centimeters (less than one inch) to over three meters (almost ten feet) in the Giant Gippsland Earthworm. Amongst the main earthworm species commonly found in temperate regions are the reddish coloured, deep-burrowing Lumbricus terrestris.

In temperate zone areas, the most commonly seen earthworms are lumbricids (Lumbricidae), mostly due to the recent rapid spread of a relatively small number of European species, but there are many other families, e.g. Megascolecidae, Octochaetidae, Sparganophilidae, Glossoscolecidae, etc. These other families often differ from the lumbricids in behavior, physiology and habitat.

Wormanatomy
Anatomy of the earthworm
PhloxBotAdded by PhloxBot

AnatomyEdit

Earthworms have a closed circulatory system. They have two main blood vessels that extend through the length of their body: a ventral blood vessel which leads the blood to the posterior end, and a dorsal blood vessel which leads to the anterior end. The dorsal vessel is contractile and pumps blood forward, where it is pumped into the ventral vessel by a series of "hearts" (aortic arches) which vary in number in the different taxa. A typical lumbricid will have 5 pairs of hearts; a total of 10. The blood is distributed from the ventral vessel into capillaries on the body wall and other organs and into a vascular sinus in the gut wall where gases and nutrients are exchanged. This arrangement may be complicated in the various groups by suboesophageal, supraoesophageal, parietal and neural vessels, but the basic arrangement holds in all earthworms. Earthworms eat in a unique way. Their mouth cavity connects directly into the digestive tract without any intermediate processes. Earthworms are decomposers feeding on undecayed leaf and other plant matter.

Learning in the earthwormEdit

Earthworms are capable of learning.like people are capable of so much.

ReproductionEdit

Mating earthworms
Earthworm Reproduction
PhloxBotAdded by PhloxBot

Earthworms are monoecious (both female and male organs within the same individual). They have testes, seminal vesicles and male pores which produce, store and release the sperm, and ovaries and ovipores. However, most also have one or more pairs of spermathecae (depending on the species) that are internal sacs which receive and store sperm from the other worm in copulation. Some species use external spermatophores for transfer instead. Copulation and reproduction are separate processes in earthworms. The mating pair overlap front ends ventrally and each exchanges sperm with the other. The cocoon, or egg case, is secreted by the clitellum, the external glandular band which is near the front of the worm, but behind the spermathecae. Some indefinite time after copulation, long after the worms have separated, the clitellum secretes the cocoon which forms a ring around the worm. The worm then backs out of the ring, and as it does so, injects its own eggs and the other worm's sperm into it. As the worm slips out, the ends of the cocoon seal to form a vaguely lemon-shaped incubator (cocoon) in which the embryonic worms develop. They emerge as small, but fully formed earthworms, except for lacking the sexual structures, which develop later. Some earthworm species are mostly parthenogenetic.

RegenerationEdit

Earthworms have the facility to replace or replicate lost segments, but this ability varies between species and depends on the extent of the damage. Stephenson (1930) devoted a chapter of his great monograph to this topic, while G.E. Gates spent 10 years studying regeneration in a variety of species, but “because little interest was shown”, Gates (1972) only published a few of his findings that, nevertheless, show it is theoretically possible to grow two whole worms from a bisected specimen in certain species. Gates’s reports included:

  • Eisenia fetida (Savigny, 1826) with head regeneration, in an anterior direction, possible at each intersegmental level back to and including 23/24, while tails were regenerated at any levels behind 20/21.
  • Lumbricus terrestris (Linneus, 1758) replacing anterior segments from as far back as 13/14 and 16/17 but tail regeneration was never found.
  • Perionyx excavatus (Perrier, 1872) readily regenerated lost parts of the body, in an anterior direction from as far back as 17/18, and in a posterior direction as far forward as 20/21.
  • Lampito mauritii (Kinberg, 1867) with regeneration in anterior direction at all levels back to 25/26 and tail regeneration from 30/31; head regeneration was sometimes believed to be caused by internal amputation resulting from Sarcophaga sp. larval infestation.

An unidentified Tasmanian earthworm shown growing a second head is reported here: [1].

BehaviorEdit

RainstormsEdit

  1. REDIRECT Template:Cleanup-rewrite

One often sees earthworms come to the surface in large numbers after a rainstorm. There are four theories for this behavior.

Robin eating a worm in spring
An earthworm being eaten by an American Robin.
PhloxBotAdded by PhloxBot
The first is that the waterlogged soil has insufficient oxygen for the worms, therefore, earthworms come to the surface to get the oxygen they need and breathe more easily. However, earthworms can survive underwater for several hours if there is oxygen in it, so this theory is rejected by some.

Secondly, some species (notably Lumbricus terrestris) come to the surface to mate. This behavior is, however, limited to a few species, as well as the fact that this might not be always connected to rain.

Thirdly, the worms may be using the moist conditions on the surface to travel more quickly than they can underground, thus colonizing new areas more quickly. Since the relative humidity is higher during and after rain, they do not become dehydrated. This is a dangerous activity in the daytime, since earthworms die quickly when exposed to direct sunlight with its strong UV content, and are more vulnerable to predators such as birds.

The fourth theory is that as there are many other organisms in the ground as well and they respirate as any animal does; the carbon dioxide produced dissolves into the rainwater; it forms carbonic acid and the soil becomes too acidic for the worms and they come seek neutral nourishment on the surface.

Locomotion and importance to soilEdit

Earthworms travel underground by the means of waves of muscular contractions which alternately shorten and lengthen the body. The shortened part is anchored to the surrounding soil by tiny claw-like bristles (setae) set along its segmented length. (Typically, earthworms have four pairs of setae for each segment but some genera are perichaetine, having a large number of setae on each segment.) The whole burrowing process is aided by the secretion of a slimy lubricating mucus. Worms can make gurgling noises underground when disturbed as a result of the worm moving through its lubricated tunnels as fast as it can. Earthworm activity aerates and mixes the soil, and is constructive to mineralization and nutrient uptake by vegetation. Certain species of earthworm come to the surface and graze on the higher concentrations of organic matter present there, mixing it with the mineral soil. Because a high level of organic matter mixing is associated with soil fertility, an abundance of earthworms is beneficial to the organic gardener. In fact as long ago as 1881 Charles Darwin wrote: It may be doubted whether there are any other animals which have played so important a part in the history of the world, as have these lowly creatures [1]

Special habitats Edit

While, as the name earthworm suggests, the main habitat of earthworms is in soil, the situation is more complicated than that. The brandling worm Eisenia fetida lives in decaying plant matter and manure. Arctiostrotus vancouverensis from Vancouver Island and the Olympic Peninsula is generally found in decaying conifer logs or in extremely acidic humus. Aporrectodea limicola and Sparganophilus and several others are found in mud in streams. Even in the soil species, there are special habitats, such as soils derived from serpentine which have an earthworm fauna of their own.

EcologyEdit

Earthworm populations depend on both physical and chemical properties of the soil, such as soil temperature, moisture, pH, salts, aeration and texture, as well as available food, and the ability of the species to reproduce and disperse.

One of the most important environmental factors is pH, but earthworms vary in their preferences. Most earthworms favor neutral to slightly acid soil. However, Lumbricus terrestris are still present in a pH of 5.4 and Dendrobaena octaedra at a pH of 4.3 and some Megascolecidae are present in extremely acid humic soils. Soil pH may also influence the numbers of worms that go into diapause. The more acid the soil, the sooner worms go into diapause, and remain in diapause the longest time at a pH of 6.4.

Earthworms form the base of many food chains. They are preyed upon by many species of birds, e.g. starlings, thrushes, gulls, crows, and both European Robins and American robins. Mammals such as hedgehogs and moles eat many earthworms as well. Earthworms are also eaten by many invertebrates such as ground beetles and other beetles, snails, slugs. Earthworms have many internal parasites including Protozoa, Platyhelminthes, Nematodes. They are found in many parts of earthworms' bodies such as blood, seminal vesicles, coelom, intestine, or in the cocoons.


==

Taxonomy and main geographic origins of earthwormsEdit

Main families :

ReferencesEdit

  1. Charles Darwin, The formation of vegetable mould through the action of worms, with observations on their habits

Further reading Edit

  • Abramson, C. I. (1990). Classical conditioning. Washington, DC: American Psychological Association.
  • Abramson, C. I. (1990). Habituation. Washington, DC: American Psychological Association.
  • Abramson, C. I., & Buckbee, D. A. (1995). Pseudoconditioning in earthworms (Lumbricus terrestris): Support for nonassociative explanations of classical conditioning phenomena through an olfactory paradigm: Journal of Comparative Psychology Vol 109(4) Dec 1995, 390-397.
  • Blue, J. (1976). Effect of anterior ganglia removal on phototaxis in the earthworm (Lumbriscus terrestris): Bulletin of the Psychonomic Society Vol 7(3) Mar 1976, 57-259.
  • Buchanan, J. A., & Houlihan, D. (2008). The use of in vivo desensitization for the treatment of a specific phobia of earthworms: Clinical Case Studies Vol 7(1) Feb 2008, 12-24.
  • Crist, E. (2002). The inner life of earthworms: Darwin's argument and its implications. Cambridge, MA: MIT Press.
  • Dickins, T. E. (2005). On the Aims of Evolutionary Theory: Evolutionary Psychology Vol 3 2005, 79-84.
  • Fiore, C., Tull, J. L., Zehner, S., & Ducey, P. K. (2004). Tracking and predation on earthworms by the invasive terrestrial planarian Bipalium adventitium (Tricladida, Platyhelminthes): Behavioural Processes Vol 67(3) Nov 2004, 327-334.
  • Gems, D., & Riddle, D. L. (1994). Longevity in Caenorhabditis elegans reduced by mating but not gamete production: Nature Vol 370(6490) Aug 1994, 723-725.
  • Gilpin, A. R., & Ratner, S. C. (1978). Intermodal stimulus generalization and retention of habituation in earthworms: Psychological Reports Vol 42(3, Pt 1) Jun 1978, 683-690.
  • Gilpin, A. R., Ratner, S. C., & Glanville, B. B. (1978). Stimulus generalization of contraction response to light in earthworm: Perceptual and Motor Skills Vol 47(1) Aug 1978, 230.
  • Glanville, B. B., Gilpin, A. R., & Ratner, S. C. (1979). Effects of interpolated stimulation on retention of habituation in the earthworm: Journal of General Psychology Vol 100(2) Apr 1979, 287-294.
  • Hadek, R., & Rosen, D. M. (1973). Studies in light avoidance responses in the intact, segmental and suprapharyngeal ganglion ablated lumbricus: Journal of Biological Psychology Vol 15(1) Jul 1973, 27-33.
  • Hughes, R. N. (1987). Mechanisms for turn alternation in four invertebrate species: Behavioural Processes Vol 14(1) Feb 1987, 89-103.
  • Keshavamurthy, P., & Krishnamoorthy, R. V. (1977). A circadian rhythm in the electrode-avoidance behavior of the earthworms Megascolex mauritii, Pheretima elongata, and Perionyx excavatus: Behavioral & Neural Biology Vol 20(1) May 1977, 17-24.
  • Koene, J. M., Pfortner, T., & Michiels, N. K. (2005). Piercing the partner's skin influences sperm uptake in the earthworm Lumbricus terrestris: Behavioral Ecology and Sociobiology Vol 59(2) Dec 2005, 243-249.
  • Macdonald, D. W. (1980). The red fox, Vulpes vulpes, as a predator upon earthworms, Lumbricus terrestris: Zeitschrift fur Tierpsychologie Vol 52(2) 1980, 171-200.
  • Marian, R. W., & Abramson, C. I. (1982). Technical note: Earthworm behavior in a modified running wheel: Journal of Mind and Behavior Vol 3(1) Win 1982, 67-74.
  • McFall, J. L. (1979). Earthworm giant nerve fibers: An electrophysiological and behavioral study: Dissertation Abstracts International.
  • McManus, F. E. (1979). Brain-behavior mechanisms and circadian activity in the earthworm: Dissertation Abstracts International.
  • McManus, F. E., Mendelson, T., & Wyers, E. J. (1982). The brain and central control in the earthworm: Behavioral & Neural Biology Vol 35(1) May 1982, 1-16.
  • McManus, F. E., & Wyers, E. J. (1978). A device for measuring patterns of locomotor behavior in the earthworm: Behavior Research Methods & Instrumentation Vol 10(3) Jun 1978, 398-400.
  • McManus, F. E., & Wyers, E. J. (1979). Differentiating ganglionic function in the earthworm: Journal of Comparative and Physiological Psychology Vol 93(6) Dec 1979, 1136-1144.
  • McManus, F. E., & Wyers, E. J. (1979). Olfaction and selective association in the earthworm, Lumbricus terrestris: Behavioral & Neural Biology Vol 25(1) Jan 1979, 39-57.
  • McManus, F. E., & Wyers, E. J. (1982). Induced variability in the distribution of activity over the circadian cycle: Journal of Comparative and Physiological Psychology Vol 96(6) Dec 1982, 1022-1026.
  • Michiels, N. K., Hohner, A., & Vorndran, I. C. (2001). Precopulatory mate assessment in relation to body size in the earthworm Lumbricus terrestris: Avoidance of dangerous liaisons? : Behavioral Ecology Vol 12(5) Sep-Oct 2001, 612-618.
  • Miller, D. B., & Tallarico, R. B. (1972). Acquisition, extinction, and spontaneous recovery of a positively reinforced approach response in the earthworm, Lumbricus terrestris: Psychological Record Vol 22(3) Sum 1972, 381-386.
  • Mizutani, K., Shimoi, T., Ogawa, H., Kitamura, Y., & Oka, K. (2004). Modulation of motor patterns by sensory feedback during earthworm locomotion: Neuroscience Research Vol 48(4) Apr 2004, 457-462.
  • Mulder, C., Hendriks, J., Baerselman, R., & Posthuma, L. (2007). Age structure and senescence in long-term cohorts of Eisenia andrei (Oligochaeta: Lumbricidae): Journals of Gerontology: Series A: Biological Sciences and Medical Sciences Vol 62A(12) Dec 2007, 1361-1363.
  • Peretti, P. O., & Bhargava, A. (1991). Environmental influences on patterns of locomotor activity of Lumbricus terrestris: Indian Journal of Behaviour Vol 15(3) Jul 1991, 56-62.
  • Ramot, D. (2008). Quantitative analysis of neural and behavioral responses to thermal gradients in the nematode caenorhabditis elegans. Dissertation Abstracts International: Section B: The Sciences and Engineering.
  • Ratner, S. C., & Gilpin, A. R. (1974). Habituation and retention of habituation of responses to air puff of normal and decerebrate earthworms: Journal of Comparative and Physiological Psychology Vol 86(5) May 1974, 911-918.
  • Rosenkoetter, J. S. (1977). Earthworm learning: Dissertation Abstracts International.
  • Smith, G. E. (1973). Discriminated approach-avoidance learning by the earthworm, Lumbricus terrestris: Dissertation Abstracts International Vol.
  • Toler, R. H. (1980). Rapid escape response of the earthworm Lumbricus terrestris: A study of reflex organization and habituation: Dissertation Abstracts International.
  • Ward, J. E., & Doolittle, J. H. (1973). The effect of the anterior ganglia on forward movements in the earthworm: Physiological Psychology Vol 1(2) Jun 1973, 129-132.
  • Watanabe, H., Takaya, T., Shimoi, T., Ogawa, H., Kitamura, Y., & Oka, K. (2005). Influence of mRNA and protein synthesis inhibitors on the long-term memory acquisition of classically conditioned earthworms: Neurobiology of Learning and Memory Vol 83(2) Mar 2005, 151-157.
  • Wyers, E. J., Smith, G. E., & Dinkes, I. (1974). Passive avoidance learning in the earthworm (Lumbricus terrestris): Journal of Comparative and Physiological Psychology Vol 86(1) Jan 1974, 157-163.


See also Edit

External linksEdit



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