Mesosoma

In hymenopterans of the suborder Apocrita (wasps, bees and ants), the mesosoma consists of the three thoracic segments and the first abdominal segment (the propodeum).

For historical reasons, in ants it is commonly referred to by the alternative name alitrunk.

[1][2][3] In scorpions, the mesosoma is composed of six segments and forms the first part of the abdomen, containing all of the major organs.

The first segment contains the sexual organs as well as a pair of vestigial and modified appendages forming a structure called the genital operculum.

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