Is the sister-group to the Pilidiophora and the second largest group of species, those with the mouth and proboscis opening combined anteriorly as a more or less terminal pore. They typically have very shallow, often inconspicuous oblique or vertical grooves, on the lateral margins near the middle of the head and may have a V-shaped groove encircling the body at the posterior of the head. The proboscis bears distinct armature, either in the form of a single relatively large, needle-like stylet, or as a cluster of tiny tack-like stylets set on a small support pad. The former comprises the traditional group Monostilifera; the latter, the Polystilifera (which also includes most of the pelagic forms). The stylet is used to puncture the body wall of prey and allows for easy administration of neurotoxin to paralyze the prey.