Sensilla on the palps and legs of the adult soft tick Argas persicus Oken (Ixodoidea : Argasidae) and their projections to the central nervous system

The sensory structures present on the palps and legs of adult Argas persicu s Oken (Ixodoidea: Argasidae) were studied by tight, scanning and transmiss ion electron microscopy. The number, distribution, surface morphology and t he fine structure of the prominent sensiila present on these appendages wer e determined. The palps have 2 morphologically prominent types of sensilla: one with a grooved surface of the hair and the other having a non-grooved hair. The TEM distinguishes at least 4 prominent subtypes in grooved sensil la with single or double lumina and dendrites occupying the periphery of th e central lumen or distributed all over the central lumen. Amongst the sens illa with non-grooved hair-shaft, a rare type of Olfactory Mechanoreceptive (OM) sensillum was found on the palps and the first legs of A. persicus. A t the base of the hair-shaft, the OM sensillum has 2 mechanosensory dendrit es. The hair-shaft of the sensillum has a porous cuticle, characteristic of an olfactory sensillum. The lumen of the hair-shaft is invested with branc hing dendrites from 3-8 neurons, which are surrounded by 4 sheath cells. Th e sensilla on the legs, including those present in the Haller's organ, are of at least 3 prominent categories. (i) Single walt with un-innervated hair -shaft. (ii) Single wall, multiporous sensillum with dendrites present in t he hair shaft. (iii) Double walls with spoke channels and dendrites present in the central lumen. Sensory projections from the crown of sensilla located on the distal end of the palp extend to the palpal and suboesophageal (SOG) ganglia. Projection s in the SOG extend further to the contralateral side. Sensilla in the Hall er's organ project to the first pedal ganglion and to the anterodorsal regi on of supraoesophageal ganglion. As expected, the primary sensory projectio ns from the sensilla of the other 3 legs extend to the respective pedal gan glia. (C) 1998 Elsevier Science Ltd. All rights reserved.