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The mouthparts of arthropods have evolved into a number of forms, each adapted to a different style of feeding. They are all developed, however, from the same basic form. Most of the parts used for feeding are modified, paired appendages, the exception being the labrum, which is a single, fused plate (though it was originally - and is embryonically - two structures); it is the front-most of the mouthparts and located on the midline.
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Insects
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In insects, the labrum is followed by the mandibles, the maxillae and the labium, which is a single structure evolved out of a pair of appendages like the labrum, but it still bears segmented palpi unlike the labrum. The least modified insect mouthparts are of the chewing type, as found in grasshoppers and most beetles, amongst others. In the order Hemiptera, the mouthparts are specialised for piercing and sucking. They are typified by the mouthparts of an aphid, which pierces plant tissues and sucks up the sap. A further variation is the siphoning mouthparts of butterflies and moths; here, the maxillae form a long proboscis which is coiled at rest, but can be extended to suck nectar from flowers.
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Myriapods
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Centipedes possess, in addition to their mouthparts, a pair of "poison claws" (maxillipeds), which are not considered mouthparts *.
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Crustaceans
Crustaceans possess up to three pairs of maxillipeds, as well as two pairs of maxillae and a pair of mandibles.
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Arachnids
The mouthparts of arachnids vary in having a pair of pedipalps, which are particularly prominent in the males. These are homologous with the mandibles in insects and crustaceans.
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