Scopulate hairs in male Liphistius spiders: probable contact chemoreceptors

Adult male Liphistius have dense hair pads on the ventral side of their tarsi. At first glance they appear like the adhesive scopulae, which are well known from mygalomorph spiders. However, a fine structural analysis of these scopulate hairs shows that they lack the brush-like structure with tiny “endfeet” that is typical for such adhesive hairs. Instead, the smooth hair shaft exhibits a small pore ventrally, about 8–10 µm from the blunt tip. A thin cuticular canal extends from that pore through the middle of the hair shaft and terminates about 30 µm above the hair base. Transmission electron microscopy reveals that this central canal contains about 16 delicate dendrites. The morphology of these scopulate hairs thus corresponds closely to contact chemoreceptors known from other spiders. Since these scopulate hairs occur only in adult males, they are likely involved in the perception of female pheromones.