Metasoma

[1] 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.

In apocritan 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.

[3] In other chelicerates, such as spiders, the mesosoma is fused with the metasoma to form the opisthosoma.