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.
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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.
The gaster is the bulbous posterior portion of the metasoma found in Apocrita Hymenoptera (bees, wasps and ants).
Other consistent features include a dorsal head covering (carapace) that lacks granular ridges (carinae), while the tail's upper coverings (tergites) have only one inconspicuous middle (median) ridge.