In biology, a species (plural: species) is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, the difficulty of defining species is known as the species problem. Differing measures are often used, such as similarity of DNA, morphology, or ecological niche. Presence of specific locally adapted traits may further subdivide species into "infraspecific taxa" such as subspecies (and in botany other taxa are used, such as varieties, subvarieties, and formae).
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Some articles on species:
... Most nemertean species have just one pair of nerve cords, many species have additional paired cords, and some species also have a dorsal cord ... In some species the cords lie within the skin, but in most they are deeper, inside the muscle layers ... Some species have paired cerebral organs, sacs whose only openings are to the outside ...
... Comprises 100 marine species ... Comprises about 400 species ... Includes seven species, of which six live as commensals in the mantle of large clams and one in that of a freshwater snail ...
... All species have a proboscis which lies in the rhynchocoel when inactive but everts (turns inside-out) to emerge just above the mouth and capture the animal's ... A few species with stubby bodies filter feed and have suckers at the front and back ends, with which they attach to a host ... Most nemerteans have various chemoreceptors, and on their heads some species have a number of pigment-cup ocelli, which can detect light but not form an image ...
... Nearly all non-crop, naturally occurring species observed in comparative farm land practice studies show a preference for organic farming both by abundance and ... An average of 30% more species inhabit organic farms ... Many weed species attract beneficial insects that improve soil qualities and forage on weed pests ...
... Orthopteroid species have a paurometabolous life cycle or incomplete metamorphosis ... is generally crucial in courtship, and most species have distinct songs ... The number of moults varies between species growth is also very variable and may take a few weeks to some months depending on food availability and weather conditions ...
More definitions of "species":
- (noun): (biology) taxonomic group whose members can interbreed.
Famous quotes containing the word species:
“An unjust law is itself a species of violence. Arrest for its breach is more so.”
—Mohandas K. Gandhi (18691948)
“The principle of avoiding the unnecessary expenditure of energy has enabled the species to survive in a world full of stimuli; but it prevents the survival of the aristocracy.”
—Rebecca West (18921983)
“Heaven and hell suppose two distinct species of men, the good and the bad. But the greatest part of mankind float betwixt vice and virtue.”
—David Hume (17111776)