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An earthworm is a soil-dwelling terrestrial invertebrate that belongs to the phylum Annelida. The term is the common name for the largest members of the class (or subclass , depending on the author) Oligochaeta .
Earthworm with clitellum lablelled. Close-up of the clitellum of a Lumbricus rubellus. The clitellum is a thickened glandular and non-segmented section of the body wall near the head in earthworms and leeches that secretes a viscid sac in which eggs are stored. [1]
Oligochaetes are well-segmented worms and most have a spacious body cavity (coelom) used as a hydroskeleton.They range in length from less than 0.5 mm (0.02 in) up to 2 to 3 metres (6.6 to 9.8 ft) in the 'giant' species such as the giant Gippsland earthworm (Megascolides australis) and the Mekong worm (Amynthas mekongianus).
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However, 'earthworm' can be a source of confusion since, in most of the world, other species are more typical. For example, through much of the unirrigated temperate areas of the world, the "common earthworm" is actually Aporrectodea (=Allolobophora) trapezoides, which in those areas is a similar size and dark colour to L. terrestris.
Original – Diagram of the head of an earthworm including most of its major organs Reason Meets all of the FP criteria for SVG diagrams, including being freely licensed Articles in which this image appears Earthworm, Lumbricus terrestris FP category for this image Wikipedia:Featured pictures/Sciences/Biology Creator KDS4444
Earthworms are a classic example of biological homonymous metamery – the property of repeating body segments with distinct regions. In biology, metamerism is the phenomenon of having a linear series of body segments fundamentally similar in structure, though not all such structures are entirely alike in any single life form because some of them perform special functions. [1]
This SVG diagram contains embedded raster graphics. Such images are liable to produce inferior results when scaled to different sizes (as well as possibly being very inefficient in file size). If appropriate to do so, they should be replaced with images created using vector graphics .