[Fine structural features of the sensory system in the ixodid tick Dermacentor niveus (Parasitiformes, Ixodidae)]

The main sensory organs (eyes, Haller's organ, and palpal organ) of Dermacentor niveus were examined in scanning and transmitting electron microscopes. The Haller's organ consists of a capsule with five porous SW-WP olfactory sensilla and pleomorphs; anterior pit with porous SW-WP, two grooved DW-WP, two thin NP-SW, and one conical DW-NP sensilla; four posterior DW-WP sensilla; and anterior group of SW-WP and DW-UP sensilla. Duct orifices of two dermal glands are situated near the capsule. Contact chemosensory sensilla of palps are represented by 4 DW-UP and 6 SW-UP sensilla. Eyes possess flattened lenses without the system of radial channels typical of eyes of other ixodid ticks examined. Unipolar photoreceptor cells with microvilli of rhabdomeres running in parallel to longitudinal cells axis contain basal bodies treated as rudiments of the cilia. On the whole, sensory system of D. niveus, dweller of semi-exposed habitats (floodland meadows, tugai forests, and shrub thickets of arid zones) is characterized by combination of features typical of species dwelling in exposed (deserts) and concealed (forests) habitats.