Ultrastructure of the sexually dimorphic basitarsal glands of leg I in manaosbiid harvestmen (Opiliones, Laniatores).

ABSTRACT

Chemical communication is an important aspect of arthropod biology especially for those arthropods with limited abilities to detect visual and acoustic signals. Sexually dimorphic glands are often associated with the production of pheromones, which play a role in reproductive processes. In the family Manaosbiidae (Opiliones Laniatores), males exhibit an enlarged, swollen, often fused, and spindle-like basitarsus on leg I. In this study, we provide a novel description of the morphology and ultrastructure of the glandular structures found in the proximal swollen tarsomeres of the male manaosbiid Rhopalocranaus albilineatus Roewer, 1932 and compare the external leg I morphology with that of two other manaosbiid harvestmen (Barrona williamsi Goodnight and Goodnight, 1942 and Cranellus montgomeryi Goodnight and Goodnight, 1947). The two proximal tarsomeres of the male R. albilineatus leg I contain two large, paired, acinar glands consisting of many glandular cells. Cells empty their secretory products into a large, branched epicuticular duct, which exits the leg via a pore on the ventral region. Thus, a total of four glandular structures are present within the two swollen tarsomeres and each possesses a conducting canal and pore. Finally, we discuss possible roles of these basitarsal glands in manaosbiid reproductive biology based on the present understanding of sexually dimorphic glands in other terrestrial arthropods (i.e., insects and spiders).