The Polystilifera (with many tiny stylets) are monophyletic. Species are distinguished primarily by the morphology of the stylets. The flatworms "fence" using extendable two-headed dagger-like stylets. The mouthparts were elongated, and included sharp piercing stylets, and possibly a sucking pump-like organ. Amblycera have chewing mouthparts, and Anoplura have true sucking mouthparts with stylets. The Polystilifera are armed with a pad, or shield, bearing numerous small stylets. They insert their stylets into root epidermis to feed. The stylets and the feeding tube form the modified mandibles, maxilla, and hypopharynx. The mouth is in the form of an asymmetrical mouth cone, consisting of piercing stylets. The mandibles in Phthiraptera (lice) are also modified into piercing stylets. The maxillae form needle-like structures, called stylets, which are enclosed by the labium. The stylets are needle-like projections used to penetrate plant and animal tissues. The mouthparts of tardigrades, diptera and aphids are also called stylets.