The Collaborative International Dictionary
Hypostome \Hy"po*stome\, Hypostoma \Hy*pos"to*ma\, n. [NL. hypostoma, fr. Gr. "ypo` beneath + ? mouth.] (Zo["o]l.) The lower lip of trilobites, crustaceans, etc.
n. (context anatomy English) An appendage on the mouth of some insects, arachnids, crustaceans, and hydrozoa
In zoology, the hypostome can refer to structures in distinct animal groups:
- Hypostome (trilobite), the ventral mouthpart plate in trilobites
- Hypostome (tick), the barbed attachment structure associated with the mouthparts of parasitic arachnids
- Hypostome (cnidarian), the oral tip surrounded by tentacles in hydrozoan cnidarians
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 two actions: One to remove the tick, and one to remove the remaining head section of the tick.
The hypostome is the hard mouthpart of trilobites found on the ventral side of the cephalon (head). The hypostome can be classified into three types based on whether they are permanently attached to the rostrum or not and whether they are aligned to the anterior dorsal tip of the glabella.