Definition

The posterior tagma (body region) of insects and many other arthropods, located behind the thorax or cephalothorax. In insects, it typically comprises 9–11 visible segments and houses the digestive tract, heart, reproductive organs, Malpighian tubules, and respiratory spiracles. In arachnids, the abdomen (often called the opisthosoma) is joined to the cephalothorax by a narrow pedicel and lacks antennae and legs. The abdomen is generally more flexible and variable in form than anterior tagmata, reflecting its role in respiration, excretion, reproduction, and—when modified—defense or display.

Etymology

Latin abdomen, belly

Example

In a honey bee worker, the abdomen contains the wax glands on sternites 4–7, the sting apparatus at the apex, and the heart running dorsally through the abdominal haemocoel; in a spider, the abdomen bears the spinnerets posteriorly and book lungs ventrally.

Synonyms

• opisthosoma (arachnids)

Related Terms

• tagma
• Thorax
• Cephalothorax
• opisthosoma
• Pedicel
• Spiracle
• Malpighian tubules
• sternite
• tergite
• cercus

Usage Notes

In arachnology, 'opisthosoma' is often preferred to avoid confusion with the vertebrate abdomen; in entomology, 'abdomen' is standard. Some myriapods and crustaceans also use 'abdomen' for posterior segments, though segmentation and tagmosis differ. The term is never used for the posterior body region in vertebrates within this field.