Slit sense organs on the scorpion leg (Androctonus australis L., Buthidae)

As in other arthropods the exoskeleton of arachnids is subjected to loads generated by external stimuli and behavioral activities. Far from being mere by-products of various activities such loads act as signals for mechanoreceptors capable of detecting minute displacements caused by them in the cuticle. In arachnids the slit sense organs serve in this capacity. Spiders have the most elaborate system of slit sense organs. Our previous studies clearly pointed to a functional significance of their specific location and orientation, as well as degree and type of aggregation (isolated, grouped, compound or lyriform) on respective body parts. The present study extends our work to the slit sense organs of scorpions. It gives a detailed account of the topography of the organs on the walking legs. In general slits are less orderly arranged on the legs of scorpions than on those of spiders. In the scorpion they never aggregate to form lyriform organs. Instead there are groups at comparable locations forming much more irregular, but still specific patterns. Isolated slits are more numerous on the scorpion leg, but are also less regularly distrubuted there. A common feature of the majority of slits on both the spider and the scorpion leg is their position on the lateral surfaces and their orientation roughly parallel to the long axis of the leg.