The anterior end of acanthocephalans contains the structures used to attach to the intestinal wall of the definitive host. The body wall, here stained yellow, is fairly thick. Small, bright yellow circles visible on the inner margins of the body wall are actually views through the lacunar system.
At the anterior and of the worm is a tubular proboscis, which is partially protruding. The proboscis is covered with geometrically arranged rows of recurved hooks. Posterior to the proboscis is a dark, oval proboscis sheath into which the proboscis can withdraw. The body wall meets the proboscis at its neck; the point where the proboscis and proboscis sheath meet. On either side of the proboscis sheath are two dark, ribbon-like lemnisci which continue to the right side of the photo. The lemnisci are hollow and are connected to the lacunar system near the neck. The wide structure attached to the posterior end of the proboscis sheath and continuing to the right side of the photo is a ligament sac. In archiacanthocephalans the ligament sac persists in adult female worms (the small black ovals within the ligament sac in this photo are eggs).