Pauropoda
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Pauropoda is a class of small, pale, millipede-like arthropods in the subphylum Myriapoda. More than 900 species in twelve families<ref name=":2">Template:Cite web</ref><ref>Template:Cite journal</ref><ref name=":0">Template:Cite web</ref> are found worldwide, living in soil and leaf mold. Pauropods look like centipedes or millipedes and may be a sister group of the latter,<ref name=Gillott2005>Template:Cite book</ref> but a close relationship with Symphyla has also been posited.<ref>Template:Cite journal</ref><ref name=":2" /> The name Pauropoda derives from the Greek pauros (meaning "small" or "few") and pous, genitive podos (meaning "foot"), because most species in this class have only nine pairs of legs as adults, a smaller number than those found among adults in any other class of myriapods.<ref>Template:Cite web</ref><ref name=":1" /><ref name=":9">Template:Cite book</ref>
Anatomy
Pauropods are soft, cylindrical animals with bodies measuring only 0.3 to 2 mm in length.<ref name=":1" /><ref name="Gillott2005" /> They have neither eyes nor hearts, although they do have sensory organs which can detect light. The body segments have ventral tracheal/spiracular pouches forming apodemes similar to those in millipedes and Symphyla, although the trachea usually connected to these structures are absent in most species. There are five pairs of long sensory hairs (trichobothria) located throughout the body segments.<ref>THE PAUROPODA - Savannah River Ecology Laboratory</ref> Pauropods can be identified because of their distinctive anal plate, which is unique to pauropods. Different species of pauropods can be identified based on the size and shape of their anal plate. The antennae are branching, biramous, and segmented, which is distinctive for the group.<ref name="Coleman">Template:Cite book</ref> Pauropods are usually either white or brown.<ref name=":2" />
Discovery
The first pauropod species to be discovered and described was Pauropus huxleyi, found by Lord Avebury in his own garden in London in 1866.<ref name=":6">Template:Cite book</ref><ref>Pauropoda (Myriapoda), a class new to the Dutch fauna, with the description of a new species</ref> He wrote of the creature:
Pauropus huxleyi is a bustling, active, neat and cleanly creature. It has, too, a look of cheerful intelligence, which forms a great contrast to the dull stupidity of the Diplopods, or the melancholy ferocity of most Chilopods.<ref name=":6" />'
In 1870, Packard discovered a species of North American pauropod, extending the group's range.<ref>Template:Cite book</ref>
Evolution and systematics
Only one fossil species has been reported: Eopauropus balticus a prehistoric species of pauropod that was found in Baltic Amber.<ref name=":2" />
Pauropods are divided into two orders: Hexamerocerata and Tetramerocerata. Hexamerocerata contains only one family, Millotauropodidae, with a single genus and only eight species.<ref>Template:Cite web</ref><ref name=":7" /> Tetramerocerata is much larger and more diverse, with eleven families, including Pauropodidae, Brachypauropodidae, and Eurypauropodidae.<ref name=":1" /><ref>Template:Cite web</ref> The family Pauropodidae is especially large, with 27 genera and 814 species,<ref>Template:Cite web</ref> including most of the genera and species in the class Pauropoda.<ref name=":0" />
Adults in the order Tetramerocerata have a scarcely telescopic antennal stalk with four segments, five or six tergites, and eight to ten pairs of legs.<ref name=":1" /> Pauropods in this order are small (sometimes quite small) and white or brownish.<ref name=":8">Template:Cite web</ref> Most species have nine pairs of legs as adults,<ref name=":9" /><ref name="Ax">Template:Cite book</ref> but adults in four genera (Cauvetauropus, Aletopauropus, Zygopauropus, and Amphipauropus) have only eight pairs of legs,<ref name=":1">Template:Cite book</ref> and adult females in the genus Decapauropus have either nine or ten pairs of legs.<ref name=":7">Template:Cite journal</ref> The order Tetramerocerata has a subcosmopolitan distribution.<ref name=":7" />
Pauropods in the order Hexamerocerata have a strongly telescopic antennal stalk with six segments.<ref name=":7" /> Adults in this order have twelve tergites and eleven pairs of legs.<ref name=":1" /> The pauropods in this order are white and relatively long and large.<ref name=":8" /> The order Hexamerocerata has a mainly tropical range.<ref name=":1" />
Reproduction and development
Pauropods, like all other myriapods, are gonochoric.<ref>Template:Cite web</ref> Male pauropods place small packets of sperm on the ground, which the females use to impregnate themselves.<ref name=":2" /> The females then deposit the fertilized eggs on the ground.<ref name=":4">Template:Cite web</ref> Parthogenesis can occur in some species, especially when environmental conditions are unfavourable.<ref name=":2" /><ref name=":5">Template:Cite web</ref>
The embryo goes through a short pupoid stage before the egg hatches and the first larval instar emerges. Juveniles then develop into adults through a series of molts, adding legs at each stage. Juveniles in the order Tetramerocerata start with three pairs of legs and progress through instars with five, then six, and then eight leg pairs, and in most species, become adults with nine leg pairs. In contrast, the first instar in the order Hexamerocerata has six leg pairs of legs and becomes an adult with eleven leg pairs. In at least some species in each order, adults continue to molt but no longer add legs or segments.<ref name=":1" /> This mode of development is known as hemianamorphosis.<ref>Template:Cite journal</ref>
Behavior and diet
Paurapods have a distinctive method of movement characterized by bursts of speed and frequent changes of direction.<ref name=":2" /> Pauropods are shy of light and will attempt to distance themselves from it.<ref name=Myriapoda>Template:Cite book</ref> Pauropods live in the soil, usually at densities of less than 100 per square metre (9/sq ft), and under debris and leaf litter.<ref name="Coleman" /><ref>Template:Cite web</ref><ref name=":3">Template:Cite web</ref><ref name=":2" /> Pauropods occasionally migrate upwards or downwards throughout the soil based on moisture levels. They feed on mold, fungi, and occasionally even the root hairs of plants.<ref name=":3" /> As their bodies are too soft to be able to dig and burrow, pauropods follow roots and crevices in the soil, sometimes all the way down to the surface of the groundwater.<ref name=":2" /><ref name=":4" />
Gallery
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Two pauropods of the genus Eurypauropus.
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References
Further reading
External links
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