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Protura
From Wikipedia, the free encyclopedia
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 Acerentomon doderoi
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Acerentomata
Eosentomata
Sinentomata
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The Protura, or proturans, are an order of hexapods previously treated as insects, and sometimes treated as a class [2]. They are very small (<2 mm long) soil-dwelling animals and are unique among arthropods for showing anamorphic development, whereby body segments are added during moults [3]. A total of around 500 species have been described worldwide, in four to eight families [1], making Protura the smallest class in the phylum Arthropoda [4].
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Proturans have no eyes, wings or antennae and lack pigmentation: they are usually white or pale brown. The sensory function of the antennae is fulfilled by the first of three pairs of five-segmented legs, which are held pointing forwards and have many tarsal sensilla and sensory hairs [5]. The head is conical, and bear two pseudoculi which are used for sensing light and may be the remnants of eyes [4]. The body is elongate and cylindrical [6]. The mouthparts are endognathous (enclosed within the head capsule) and consist of thin mandibles and maxillae [3]. There are no cerci at the end of the abdomen, which gives the group their name, from the Greek proto- (meaning "first", in this case implying primitive), and our, meaning "tail" [4]. The first three abdominal segments bear limb-like appendages [5] called "styli" [4]. The genitalia are internal and the genital opening lies between the eleventh segment and the telson of the adult[5]. Members of Eosentomoidea possess spiracles and a simple tracheal system while those in the Acerentomoidea lack these structures and perform gas exchange by diffusion [5].
Proturans live chiefly in soil, moss and leaf litter [3] of moist temperate forests [4] which are not too acidic [7], but have also been found beneath rocks or under the bark of trees [6], as well as in animal burrows [5]. They are generally restricted to the uppermost 10 cm [7], but have been found as deep as 10 inches (25 cm)[1]. Although they are sometimes considered uncommon [4], they are probably often overlooked because of their small size [6], and densities of over 90,000 individuals per square metre have been measured [8].
The diet of proturans is uncertain, but they are feed on mycorrhizal fungi, dead Acari, and mushroom powder in culture [5] and are thought to feed on decaying vegetable matter and fungi in the wild [6][4]. The styliform mouthparts suggest that Protura are fluid feeders and there is evidence that some species suck out the contents of fungal hyphae [7].
Proturans which live near the soil surface generally have one generation per year and have longer legs while those that live deeper have shorter legs and reproduce less seasonally, although there are also migratory species which move to deeper layers for the winter and shallower layers for the summer [7]
The larva has nine abdominal segments, but the number increases through moulting until the full adult number of twelve is reached. This process of anamorphosis is not found in any other group of arthropods. Further moults may occur, but do not involve any additional body segments [4], and it is not known whether the adults continue to moult throughout their lives [5]. Eggs have only been observed in a few species [5]. Five developmental stages follow: the prelarva hatches from the egg and has only weakly developed mouthparts and nine abdominal segments; larva I follows and has fully developed mouthparts; larva II has ten adbominal segments; maturus junior has twelve abdominal segments and is followed by the adult [5]. The family Acerentomidae differs in having an extra pre-imago stage, with partially developed genitalia, between the maturus junior and the adult [5].
Proturans were first discovered in the early twentieth century, when Filippo Silvestri and Antonio Berlese discovered the animals independently [7]. The first species to be described was Acerentomon doderoi, published in 1907 by Silvestri [5] based on material from near Syracuse, New York [4].
- ^ a b c Protura. Tree of Life Web Project (2002-01-01).
- ^ Charles S. Henry (2005). Insect phylogeny. University of Connecticut.
- ^ a b c P. J. Gullan & P. S. Cranston. The insects: an outline of entomology. Chapman and Hall. ISBN 0-412-49360-8.
- ^ a b c d e f g h i John R. Meyer (2005-03-05). Protura. North Carolina State University.
- ^ a b c d e f g h i j k Christopher Tipping (2004). Proturans. University of Florida.
- ^ a b c d Protura. CSIRO.
- ^ a b c d e Gordon's Protura Page (2005-11-11).
- ^ Krauß, J. & W. Funke (1999). Extraordinary high density of Protura in a windfall area of young spruce plants. Pedobiologia 43: 44–46.