Achterlijf

Achterlijf is a Dutch anatomical term that refers to the hind part of an animal’s body, typically the abdomen or posterior tagma. It is used mainly in zoological descriptions of arthropods and serves as the counterpart to voorlijf, the anterior body part that includes the head and, in many groups, the thorax. In spiders, for example, the achterlijf corresponds to the opisthosoma, the posterior body region. In crustaceans and other arthropods, it denotes the abdominal segments that follow the thorax and house a range of organs.

The exact composition and boundaries of the achterlijf vary among groups, reflecting differences in tagmosis (the specialization of body segments). The achterlijf generally contains portions of the digestive and reproductive systems and may bear specialized appendages or openings depending on the taxon. In crustaceans, abdominal appendages called pleopods may be part of the achterlijf, while in spiders the opisthosoma is the posterior segment that carries features such as spinnerets in many species.

Etymology and usage: the term combines achter ('behind') and lijf ('body') and is primarily found in Dutch scientific literature. It is less common in everyday language and is not typically used to describe human anatomy, where terms like buik or rug are more common. The concept of a front (voorlijf) and back (achterlijf) body part is useful in comparative anatomy to illustrate how different animals segment their bodies. See also voorlijf.