gnathosoma

The gnathosoma is the anterior mouthpart–bearing region of arachnids in the subclass Acari, which includes mites and ticks. It houses the feeding apparatus and is distinct from the main body segment called the idiosoma.

In most Acari, the gnathosoma comprises the chelicerae and pedipalps, and often includes the hypostome, a structure involved in feeding and, in many ticks, in anchoring the mouthparts to a host. The exact arrangement of these mouthparts varies among taxa, and in some mites the gnathosoma is relatively compact or more mobile relative to the rest of the body.

The primary function of the gnathosoma is feeding. Depending on the species, the mouthparts support piercing, cutting, or sucking actions to acquire nutrients from a host or from environmental resources. In ticks, the gnathosoma (often referred to as the capitulum) is the main apparatus used during attachment and blood feeding. In free-living or predatory mites, the same region serves a similar feeding role but against prey or substrates.

Morphological variation in the gnathosoma is a common characteristic used in the taxonomy and identification of Acari. Differences in the size, shape, and arrangement of the chelicerae, pedipalps, and hypostome reflect ecological adaptations and evolutionary relationships. The gnathosoma thus provides insight into the feeding strategies and evolutionary diversity of mites and ticks.