High diversity and population structure in a widespread tarantula Sickius longibulbi (Mygalomorphae: Theraphosidae)

Sickius Soares & Camargo, 1948 is a monotypic genus (Sickius longibulbi) characterized by a broad geographic distribution across Brazil and conservative morphology. Notably, females lack spermathecae, and males possess palpal bulb with a long embolus, both traits with taxonomic importance. The genus belongs to the infraorder Mygalomorphae, a group with intricate taxonomic challenges due to uniform morphology, complicating species delimitation. In the present study, we employed an integrative taxonomic approach, combining mitochondrial DNA sequences of the Cytochrome Oxidase I (COI) gene with Fourier Elliptical Analysis of the male palpal bulb shape to investigate lineage differentiation and evolutionary patterns within the genus Sickius. We observed genetic structured populations along with morphometric variation and geographic distribution, except for the two lineages localized in northeast Cerrado. We retain S. longibulbi as a single species with great diversity and possibly undergoing a process of divergence. Future studies with larger sample sizes are encouraged to confirm these findings and further investigate the evolutionary history of the genus.