Accessing the challenges of descriptive morphology in Barychelidae and Theraphosidae through a morphometric approach (Araneae, Mygalomorphae)

Abstract Phylogenetic studies have confirmed that Barychelidae is a sister group of Theraphosidae. However, taxonomic instability has led to the transfer of genera between the two families, both families show overlapping diagnostic characteristics, indicating a similarity making species differentiation challenging. In this study, we conducted an evaluation of three morphological characters that are commonly used to distinguish Barychelidae and Theraphosidae. We employed geometric morphometric to analyze variations in the shapes of the maxilla, labium, and the eyes arrangement. Our results revealed that these characters show continuous variation, which can make it problematic for discrete categorization and differentiation between Barychelidae and Theraphosidae. On the other hand, our analysis showed that the shape of the eye arrangement is effective in distinguishing the subfamilies within Barychelidae. Furthermore, we found notable distinctions between these characters on the Neotropical Sasoninae genera compared to the Sason Simon, 1887. Therefore, highlights the importance of incorporation of morphometric analyses into taxonomic and cladistics studies to improve the understanding of distinctions between families that are considered as sister groups.