Final answer:
The correct answer is a. Hypostome. Mites and ticks, as chelicerates, have adapted mouthparts including the hypostome for their parasitic feeding habits. The chelicerae and pedipalps form vital structures for feeding and sensory functions in these organisms.
Step-by-step explanation:
The mites and ticks carry their mouthparts on a little anterior projection called the hypostome.
Mites and ticks, which are part of the subphylum Chelicerata, have unique body structures adapted for their parasitic lifestyles. Their body is divided into two tagmata: the prosoma and the opisthosoma. Chelicerata, which includes arachnids like spiders and scorpions, are named for their first pair of appendages, the chelicerae. These serve as specialized mouthparts and are a key feature in identifying members of this subphylum. The chelicerae, along with the pedipalps which are the second pair of appendages, form a preoral cavity where some species secrete digestive enzymes to pre-digest food.
In the case of parasitic chelicerates such as ticks, the hypostome is part of their blood-sucking apparatus, which they use to attach to and feed from their hosts. This adaptation is particularly significant for species that require a blood meal to complete their life cycle, such as ticks which are vectors for various diseases.