Lyriform vibration receptors in the web-building spider,Nephila clavata(Araneidae: Araneae: Arachnida)

Vibration receptors appear to be more necessary for web-building spiders, but most knowledge of arachnid lyriform organs comes from the study of wandering spiders affected by ground vibrations. Here, we examined the fine structural aspects of the lyriform organs in the web-building spiderNephila clavatausing field emission scanning electron microscopy (FESEM) to fill the gap. The lyriform organ is found in all appendages, including the femur, patella, tibia, and metatarsal segments. A number of slit receptors of various sizes are distributed in the parallel orientation of the cuticle along the long axis. According to its fine structural characteristics, all lyriform organs of this spider are classified as a compound type with multiple cuticular slits. However, the number of cuticular slits per each lyriform organ varies considerably from a minimum of three to a maximum of 17. A total 35 pairs of lyriform organs were counted from an adult female spider. Except for small numerical variation in the 4th appendage, the distribution is remarkably constant within each appendage. Comparing the total number of cuticular slits per each appendage, the 3rd appendage has the highest number (85), but the 4th appendage shows the least number (63). Based on the total number of cuticular slits per leg segment, the patella segment seems to be the most sensitive to vibration reception in this orb-web spider.