1) Arachnid anatomy 
In zoology, the hypostome can refer to structures in distinct animal groups: ...[tick] The hypostome (also called the maxilla, radula, or labium) is a calcified harpoon-like structure near the mouth area of certain parasitic arthropods including ticks, that allows them to anchor themselves firmly in place on a host mammal while sucking blood. This mechanism is normally so strong that removal of a lodged tick requires t...
• (n.) Alt. of Hypostoma
In ticks, the median ventral dart-like mouthpart that is immovably attached to basal part of the capittilum.
Portion of the mouthparts of acarines; composed of fused coxae of pedipalps.
Hy'po·stome 
Type: Term Pronunciation: hī′pō-stōm Definitions: 1. The central unpaired holdfast organ of the tick capitulum; the hypostome is covered with recurved spines that enable it to serve as an anchoring device while the tick feeds.
any of several parts or organs of the mouth, as the labrum of a crustacean.