Corniculus or Rutellum

Primitively the Acariformes and Opilioacarida have a hypertrophied and toothed seta-like structure on the margin of the hypostome called the rutellum that they use to help cut pieces of food during eating (typically the chelicerae hold the food, pull it into the mouth, and the rutella clip off the piece on either side).  In Mesostigmata and Holothyrida, a similar structure is present, but it is usually horn-like and used to support the salivary styli when they are introduced into a prey's body to discharge enzymes for external digestion.  In some several lineages of Mesostigmata and Holothyrida, the corniculi are toothed and look more like rutella.