earthworm


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earthworm,

terrestrial, cylindrical segmented worm of the class Oligochaeta. There are 2,200 earthworm species, found all over the world except in arid and arctic regions and ranging in size from 1 in. (2.5 cm) to the 11-ft (330-cm) giant worms of the tropics. Some earthworms are pallid in color, many are reddish brown to purple, and one Philippino species is bright blue. Earthworms burrow in the ground, swallowing soil from which the organic material is extracted and ground up in the gizzard and depositing the residue as castings outside the burrow. They come to the surface only on cloudy days and at night (hence the name night crawlers) unless they are flooded out by heavy rainfalls. In cold and dry weather they retreat into their burrows and remain dormant. The segments of the earthworm, visible externally as rings, are separated by internal partitions. On each segment are four pairs of bristles, or setae, with which the worm anchors itself to the walls of the burrow, drawing itself forward by rhythmic muscular contractions. There is a nerve cord, with ganglia in each segment and an enlarged cerebral ganglion (a primitive brain) at the anterior end. Although they have no prominent sense organs, earthworms are sensitive to light, touch, vibration, and chemicals. The circulatory system is enclosed in vessels; the blood (which contains hemoglobin) is pumped by muscular contractions of five linearly arranged hearts. Earthworms are hermaphroditic, but they cross-fertilize. Two worms exchange sperm cells during copulation; fertilization occurs after the worm's own eggs and the received sperm are encased in a tough sheath secreted by the clitellum, a conspicuous band of tissue near the anterior end. The sheath slips over the worm's head and is deposited underground, where it serves as a cocoon for the developing young. There is no larval stage; the young hatch as miniature adults. The common American and European earthworm, Lumbricus terrestris, up to 10 in. (25 cm) long, with about 150 segments, is used for laboratory dissection and study. Earthworms are also used as live bait and are eaten by some peoples—such as the Maoris, who consider certain species delicacies. The earthworm's greatest service, however, of immense importance to agriculture, is aerating and mixing the soil. Earthworm castings bring to the surface from 7 to 18 tons of soil per acre annually. This invaluable function of the earthworm was first pointed out in a detailed study by Charles Darwin. Earthworms are classified in the phylum AnnelidaAnnelida
[Lat., anellus=a ring], phylum of soft-bodied, bilaterally symmetrical (see symmetry, biological), segmented animals, known as the segmented, or annelid, worms.
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, class Oligochaeta, order Opisthopora.
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earthworm

[′ərth‚wərm]
(invertebrate zoology)
The common name for certain terrestrial members of the class Oligochaeta, especially forms belonging to the family Lumbricidae.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

earthworm

any of numerous oligochaete worms of the genera Lumbricus, Allolobophora, Eisenia, etc., which burrow in the soil and help aerate and break up the ground
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005
References in periodicals archive ?
Nutrient status of vermicompost of urban green waste processed by three earthworm species- Eisenia fetida, Eudrilus eugeniae and Perionyx excavates.
A few years ago, while conducting a study in northern Alberta to see how the forest floor was recovering after oil and gas activity, she saw something she had never seen there before: earthworms. "I was amazed," she said.
The new "Earthworm Jim" game will be released exclusively for the upcoming Intellivision Amico Console, a new gaming system designed with "togetherness as its core."  The new console will be released on Oct.
'Earthworms and black soldier flies decompose the waste, adding fertility to the soil.
There were no cocoons containing broken or dead earthworm tissues within the 20 and 30 C treatment groups.
Therefore, in this paper we aimed to verify the effectiveness of sieves with different mesh sizes in retaining earthworm chaetae, and provide some methodological recommendations for improving the precise assessment of the contribution of earthworms to carnivore diets.
Water-stable macroaggregates and microaggregates and silt and clay were significantly affected by earthworm and AMF x earthworm interactions (P<0.05, Table 1).
Rearing and culturing of earthworm. The procured earthworm was kept in the laboratory at around 20-25 [degrees]C with a humidity level above 80%, for the process of rearing.
Lumbrokinase is a mixture of enzymes from earthworms, thus products manufactured by different companies will have slightly different properties due to the differences in earthworm species used, extraction methods, and purification processes.
New Delhi [India], Aug 19 ( ANI ): A team of Indian researchers has discovered two new primitive species of earthworm in the Western Ghats mountain ranges in Kerala.
In this complex set of contexts, we have found it interesting to contribute to studying the interaction between physical and physicochemical properties of soil and the properties of earthworm community in El Madher region, where soils are cultivated and irrigated by the partially treated waters of El Gourzi effluent and are in incessant extension.