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The METASOMA is the posterior part of the body, or tagma , of arthropods whose body is composed of three parts, the other two being the prosoma and the mesosoma . In insects, it contains most of the digestive tract , respiratory system , and circulatory system , and the apical segments are typically modified to form genitalia . In a few of the most primitive insects (the Archaeognatha ), the metasomal segments bear small, articulated appendages called "styli", which are often considered to be vestigial . There are also pre-apical appendages in most insect orders, called cerci , which may be multi-segmented and almost resembling a posterior pair of antennae ; these may be variously modified, or lost entirely. Otherwise, most adult insects lack appendages on the metasoma, though many larval insects (e.g., caterpillars ) have some form of appendages, such as prolegs or, in aquatic insects, gills .

In apocritan Hymenoptera
Hymenoptera
(wasps , bees and ants ), the metasoma consists of the second abdominal segment (which typically forms a petiole ) and those segments posterior to it, and is often called the gaster rather than referring to it as the "abdomen"; in these insects, the first abdominal segment is called the propodeum and is fused to the thorax . The metasoma is armoured with chitinous plates on the upper surface by the tergites and on the lower surface by the sternites .

In scorpions , the metasoma is the tail. In other chelicerates, such as spiders , the mesosoma is fused with the metasoma to form the opisthosoma .

REFERENCES

* ^ A B D. R. Khanna & P. R. Yadav (2004). "Segmentation in arthropods". Biology of Arthropoda. Discovery Publishing House . pp. 316–394. ISBN 978-81-7141-897-8 . * ^ Donald L. J. Quicke (2009). " Hymenoptera
Hymenoptera
(ants, bees, wasps)". In Vincent H. Resh & Ring T. Cardé. Encyclopedia of Insects (2nd ed.). Academic Press . pp. 473–484. ISBN 978-0-12-374144-8 . * ^ Stanley C. Williams (2009). "Scorpions". In Vincent H. Resh & Ring T. Cardé. Encyclopedia of Insects (2nd ed.). Academic Press . pp. 904–909. ISBN 978-0-12-374144-8 .

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